diff --git a/src/main/java/com/google/api/generator/engine/ast/TypeNode.java b/src/main/java/com/google/api/generator/engine/ast/TypeNode.java
index aef8f15727..46403071e1 100644
--- a/src/main/java/com/google/api/generator/engine/ast/TypeNode.java
+++ b/src/main/java/com/google/api/generator/engine/ast/TypeNode.java
@@ -65,6 +65,9 @@ public enum TypeKind {
   public static final TypeNode SHORT_OBJECT =
       withReference(ConcreteReference.withClazz(Short.class));
 
+  public static final TypeNode CLASS_OBJECT =
+      withReference(ConcreteReference.withClazz(Class.class));
+
   public static final TypeNode BYTESTRING =
       TypeNode.withReference(ConcreteReference.withClazz(ByteString.class));
 
diff --git a/src/main/java/com/google/api/generator/gapic/composer/MockServiceImplClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/MockServiceImplClassComposer.java
index efdff56e6a..d76ee0bc1c 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/MockServiceImplClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/MockServiceImplClassComposer.java
@@ -56,6 +56,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 import javax.annotation.Generated;
 
@@ -484,13 +485,55 @@ private static Statement createHandleObjectStatement(
     }
 
     TypeNode exceptionType = TypeNode.withReference(ConcreteReference.withClazz(Exception.class));
+    Expr actualResponseTypeString =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(
+                MethodInvocationExpr.builder()
+                    .setExprReferenceExpr(localResponseVarExpr)
+                    .setMethodName("getClass")
+                    .build())
+            .setMethodName("getName")
+            .setReturnType(TypeNode.STRING)
+            .build();
+    Function<TypeNode, Expr> typeToStrFn =
+        t ->
+            MethodInvocationExpr.builder()
+                .setExprReferenceExpr(
+                    VariableExpr.builder()
+                        .setStaticReferenceType(t)
+                        .setVariable(
+                            Variable.builder()
+                                .setType(TypeNode.CLASS_OBJECT)
+                                .setName("class")
+                                .build())
+                        .build())
+                .setMethodName("getName")
+                .setReturnType(TypeNode.STRING)
+                .build();
+    Expr expectedResponseTypeOneString = typeToStrFn.apply(protoMethod.outputType());
+    Expr expectedResponseTypeTwoString = typeToStrFn.apply(exceptionType);
+
     Expr newExceptionExpr =
         NewObjectExpr.builder()
             .setType(
                 TypeNode.withReference(ConcreteReference.withClazz(IllegalArgumentException.class)))
             .setArguments(
-                Arrays.asList(
-                    ValueExpr.withValue(StringObjectValue.withValue("Unrecognized response type"))))
+                // Generates something like:
+                // String.format("Unrecognized response type %s, expected %s or %s",
+                //     Operation.class.getName(), Exception.class.getName());
+                MethodInvocationExpr.builder()
+                    .setStaticReferenceType(TypeNode.STRING)
+                    .setMethodName("format")
+                    .setArguments(
+                        ValueExpr.withValue(
+                            StringObjectValue.withValue(
+                                "Unrecognized response type %s for method "
+                                    + protoMethod.name()
+                                    + ", expected %s or %s")),
+                        actualResponseTypeString,
+                        expectedResponseTypeOneString,
+                        expectedResponseTypeTwoString)
+                    .build())
             .build();
 
     return IfStatement.builder()
diff --git a/src/main/java/com/google/api/generator/gapic/composer/RetrySettingsComposer.java b/src/main/java/com/google/api/generator/gapic/composer/RetrySettingsComposer.java
index 0118d43eb1..77253189d2 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/RetrySettingsComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/RetrySettingsComposer.java
@@ -316,10 +316,7 @@ public static Expr createLroSettingsBuilderExpr(
         t ->
             VariableExpr.builder()
                 .setVariable(
-                    Variable.builder()
-                        .setType(TypeNode.withReference(ConcreteReference.withClazz(Class.class)))
-                        .setName("class")
-                        .build())
+                    Variable.builder().setType(TypeNode.CLASS_OBJECT).setName("class").build())
                 .setStaticReferenceType(t)
                 .build();
     builderSettingsExpr =
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientTestClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientTestClassComposer.java
index 0b27868b1c..3b3bd8cddb 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientTestClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientTestClassComposer.java
@@ -1561,11 +1561,7 @@ private static List<Statement> createRpcLroExceptionTestCatchBody(
 
     Expr testExpectedValueExpr =
         VariableExpr.builder()
-            .setVariable(
-                Variable.builder()
-                    .setType(TypeNode.withReference(ConcreteReference.withClazz(Class.class)))
-                    .setName("class")
-                    .build())
+            .setVariable(Variable.builder().setType(TypeNode.CLASS_OBJECT).setName("class").build())
             .setStaticReferenceType(FIXED_TYPESTORE.get("InvalidArgumentException"))
             .build();
     Expr getCauseExpr =
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceStubSettingsClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceStubSettingsClassComposer.java
index 45317be985..2774b90c3e 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceStubSettingsClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceStubSettingsClassComposer.java
@@ -999,11 +999,7 @@ private static List<MethodDefinition> createDefaultHelperAndGetterMethods(
             .setArguments(
                 VariableExpr.builder()
                     .setVariable(
-                        Variable.builder()
-                            .setType(
-                                TypeNode.withReference(ConcreteReference.withClazz(Class.class)))
-                            .setName("class")
-                            .build())
+                        Variable.builder().setType(TypeNode.CLASS_OBJECT).setName("class").build())
                     .setStaticReferenceType(
                         typeStore.get(ClassNames.getServiceStubSettingsClassName(service)))
                     .build())
diff --git a/src/test/java/com/google/api/generator/gapic/composer/goldens/MockEchoImpl.golden b/src/test/java/com/google/api/generator/gapic/composer/goldens/MockEchoImpl.golden
index 779c195f71..6d78ee2827 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/goldens/MockEchoImpl.golden
+++ b/src/test/java/com/google/api/generator/gapic/composer/goldens/MockEchoImpl.golden
@@ -53,7 +53,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method Echo, expected %s or %s",
+                  response.getClass().getName(),
+                  EchoResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -67,7 +73,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method Expand, expected %s or %s",
+                  response.getClass().getName(),
+                  EchoResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -84,7 +96,13 @@ public class MockEchoImpl extends EchoImplBase {
             } else if (response instanceof Exception) {
               responseObserver.onError(((Exception) response));
             } else {
-              responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+              responseObserver.onError(
+                  new IllegalArgumentException(
+                      String.format(
+                          "Unrecognized response type %s for method Collect, expected %s or %s",
+                          response.getClass().getName(),
+                          EchoResponse.class.getName(),
+                          Exception.class.getName())));
             }
           }
 
@@ -114,7 +132,13 @@ public class MockEchoImpl extends EchoImplBase {
             } else if (response instanceof Exception) {
               responseObserver.onError(((Exception) response));
             } else {
-              responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+              responseObserver.onError(
+                  new IllegalArgumentException(
+                      String.format(
+                          "Unrecognized response type %s for method Chat, expected %s or %s",
+                          response.getClass().getName(),
+                          EchoResponse.class.getName(),
+                          Exception.class.getName())));
             }
           }
 
@@ -145,7 +169,13 @@ public class MockEchoImpl extends EchoImplBase {
             } else if (response instanceof Exception) {
               responseObserver.onError(((Exception) response));
             } else {
-              responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+              responseObserver.onError(
+                  new IllegalArgumentException(
+                      String.format(
+                          "Unrecognized response type %s for method ChatAgain, expected %s or %s",
+                          response.getClass().getName(),
+                          EchoResponse.class.getName(),
+                          Exception.class.getName())));
             }
           }
 
@@ -173,7 +203,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method PagedExpand, expected %s or %s",
+                  response.getClass().getName(),
+                  PagedExpandResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -188,7 +224,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method SimplePagedExpand, expected %s or %s",
+                  response.getClass().getName(),
+                  PagedExpandResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -202,7 +244,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method Wait, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -216,7 +264,13 @@ public class MockEchoImpl extends EchoImplBase {
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method Block, expected %s or %s",
+                  response.getClass().getName(),
+                  BlockResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/asset/MockAssetServiceImpl.java b/test/integration/goldens/asset/MockAssetServiceImpl.java
index 1ef582b272..46798d0326 100644
--- a/test/integration/goldens/asset/MockAssetServiceImpl.java
+++ b/test/integration/goldens/asset/MockAssetServiceImpl.java
@@ -71,7 +71,13 @@ public void exportAssets(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ExportAssets, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -87,7 +93,13 @@ public void batchGetAssetsHistory(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method BatchGetAssetsHistory, expected %s or %s",
+                  response.getClass().getName(),
+                  BatchGetAssetsHistoryResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -101,7 +113,11 @@ public void createFeed(CreateFeedRequest request, StreamObserver<Feed> responseO
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateFeed, expected %s or %s",
+                  response.getClass().getName(), Feed.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -115,7 +131,11 @@ public void getFeed(GetFeedRequest request, StreamObserver<Feed> responseObserve
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetFeed, expected %s or %s",
+                  response.getClass().getName(), Feed.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -130,7 +150,13 @@ public void listFeeds(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListFeeds, expected %s or %s",
+                  response.getClass().getName(),
+                  ListFeedsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -144,7 +170,11 @@ public void updateFeed(UpdateFeedRequest request, StreamObserver<Feed> responseO
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateFeed, expected %s or %s",
+                  response.getClass().getName(), Feed.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -158,7 +188,13 @@ public void deleteFeed(DeleteFeedRequest request, StreamObserver<Empty> response
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteFeed, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -174,7 +210,13 @@ public void searchAllResources(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method SearchAllResources, expected %s or %s",
+                  response.getClass().getName(),
+                  SearchAllResourcesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -190,7 +232,13 @@ public void searchAllIamPolicies(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method SearchAllIamPolicies, expected %s or %s",
+                  response.getClass().getName(),
+                  SearchAllIamPoliciesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/credentials/MockIAMCredentialsImpl.java b/test/integration/goldens/credentials/MockIAMCredentialsImpl.java
index 851402cad9..be2f309d7c 100644
--- a/test/integration/goldens/credentials/MockIAMCredentialsImpl.java
+++ b/test/integration/goldens/credentials/MockIAMCredentialsImpl.java
@@ -70,7 +70,13 @@ public void generateAccessToken(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GenerateAccessToken, expected %s or %s",
+                  response.getClass().getName(),
+                  GenerateAccessTokenResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -85,7 +91,13 @@ public void generateIdToken(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GenerateIdToken, expected %s or %s",
+                  response.getClass().getName(),
+                  GenerateIdTokenResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -99,7 +111,13 @@ public void signBlob(SignBlobRequest request, StreamObserver<SignBlobResponse> r
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method SignBlob, expected %s or %s",
+                  response.getClass().getName(),
+                  SignBlobResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -113,7 +131,13 @@ public void signJwt(SignJwtRequest request, StreamObserver<SignJwtResponse> resp
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method SignJwt, expected %s or %s",
+                  response.getClass().getName(),
+                  SignJwtResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/library/MockLibraryServiceImpl.java b/test/integration/goldens/library/MockLibraryServiceImpl.java
index f9c59c9467..ff65534071 100644
--- a/test/integration/goldens/library/MockLibraryServiceImpl.java
+++ b/test/integration/goldens/library/MockLibraryServiceImpl.java
@@ -84,7 +84,13 @@ public void createShelf(CreateShelfRequest request, StreamObserver<Shelf> respon
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateShelf, expected %s or %s",
+                  response.getClass().getName(),
+                  Shelf.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -98,7 +104,13 @@ public void getShelf(GetShelfRequest request, StreamObserver<Shelf> responseObse
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetShelf, expected %s or %s",
+                  response.getClass().getName(),
+                  Shelf.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -113,7 +125,13 @@ public void listShelves(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListShelves, expected %s or %s",
+                  response.getClass().getName(),
+                  ListShelvesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -127,7 +145,13 @@ public void deleteShelf(DeleteShelfRequest request, StreamObserver<Empty> respon
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteShelf, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -141,7 +165,13 @@ public void mergeShelves(MergeShelvesRequest request, StreamObserver<Shelf> resp
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method MergeShelves, expected %s or %s",
+                  response.getClass().getName(),
+                  Shelf.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -155,7 +185,11 @@ public void createBook(CreateBookRequest request, StreamObserver<Book> responseO
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateBook, expected %s or %s",
+                  response.getClass().getName(), Book.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -169,7 +203,11 @@ public void getBook(GetBookRequest request, StreamObserver<Book> responseObserve
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetBook, expected %s or %s",
+                  response.getClass().getName(), Book.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -184,7 +222,13 @@ public void listBooks(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListBooks, expected %s or %s",
+                  response.getClass().getName(),
+                  ListBooksResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -198,7 +242,13 @@ public void deleteBook(DeleteBookRequest request, StreamObserver<Empty> response
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteBook, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -212,7 +262,11 @@ public void updateBook(UpdateBookRequest request, StreamObserver<Book> responseO
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateBook, expected %s or %s",
+                  response.getClass().getName(), Book.class.getName(), Exception.class.getName())));
     }
   }
 
@@ -226,7 +280,11 @@ public void moveBook(MoveBookRequest request, StreamObserver<Book> responseObser
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method MoveBook, expected %s or %s",
+                  response.getClass().getName(), Book.class.getName(), Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/logging/MockConfigServiceV2Impl.java b/test/integration/goldens/logging/MockConfigServiceV2Impl.java
index 53fcedc2f8..fdbf74ac4d 100644
--- a/test/integration/goldens/logging/MockConfigServiceV2Impl.java
+++ b/test/integration/goldens/logging/MockConfigServiceV2Impl.java
@@ -92,7 +92,13 @@ public void listBuckets(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListBuckets, expected %s or %s",
+                  response.getClass().getName(),
+                  ListBucketsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -106,7 +112,13 @@ public void getBucket(GetBucketRequest request, StreamObserver<LogBucket> respon
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetBucket, expected %s or %s",
+                  response.getClass().getName(),
+                  LogBucket.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -121,7 +133,13 @@ public void updateBucket(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateBucket, expected %s or %s",
+                  response.getClass().getName(),
+                  LogBucket.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -136,7 +154,13 @@ public void listSinks(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListSinks, expected %s or %s",
+                  response.getClass().getName(),
+                  ListSinksResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -150,7 +174,13 @@ public void getSink(GetSinkRequest request, StreamObserver<LogSink> responseObse
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetSink, expected %s or %s",
+                  response.getClass().getName(),
+                  LogSink.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -164,7 +194,13 @@ public void createSink(CreateSinkRequest request, StreamObserver<LogSink> respon
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateSink, expected %s or %s",
+                  response.getClass().getName(),
+                  LogSink.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -178,7 +214,13 @@ public void updateSink(UpdateSinkRequest request, StreamObserver<LogSink> respon
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateSink, expected %s or %s",
+                  response.getClass().getName(),
+                  LogSink.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -192,7 +234,13 @@ public void deleteSink(DeleteSinkRequest request, StreamObserver<Empty> response
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteSink, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -207,7 +255,13 @@ public void listExclusions(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListExclusions, expected %s or %s",
+                  response.getClass().getName(),
+                  ListExclusionsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -222,7 +276,13 @@ public void getExclusion(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetExclusion, expected %s or %s",
+                  response.getClass().getName(),
+                  LogExclusion.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -237,7 +297,13 @@ public void createExclusion(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateExclusion, expected %s or %s",
+                  response.getClass().getName(),
+                  LogExclusion.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -252,7 +318,13 @@ public void updateExclusion(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateExclusion, expected %s or %s",
+                  response.getClass().getName(),
+                  LogExclusion.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -267,7 +339,13 @@ public void deleteExclusion(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteExclusion, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -282,7 +360,13 @@ public void getCmekSettings(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetCmekSettings, expected %s or %s",
+                  response.getClass().getName(),
+                  CmekSettings.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -297,7 +381,13 @@ public void updateCmekSettings(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateCmekSettings, expected %s or %s",
+                  response.getClass().getName(),
+                  CmekSettings.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/logging/MockLoggingServiceV2Impl.java b/test/integration/goldens/logging/MockLoggingServiceV2Impl.java
index 1f65485c7a..ece59015b9 100644
--- a/test/integration/goldens/logging/MockLoggingServiceV2Impl.java
+++ b/test/integration/goldens/logging/MockLoggingServiceV2Impl.java
@@ -78,7 +78,13 @@ public void deleteLog(DeleteLogRequest request, StreamObserver<Empty> responseOb
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteLog, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -93,7 +99,13 @@ public void writeLogEntries(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method WriteLogEntries, expected %s or %s",
+                  response.getClass().getName(),
+                  WriteLogEntriesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -108,7 +120,13 @@ public void listLogEntries(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListLogEntries, expected %s or %s",
+                  response.getClass().getName(),
+                  ListLogEntriesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -124,7 +142,13 @@ public void listMonitoredResourceDescriptors(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListMonitoredResourceDescriptors, expected %s or %s",
+                  response.getClass().getName(),
+                  ListMonitoredResourceDescriptorsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -138,7 +162,13 @@ public void listLogs(ListLogsRequest request, StreamObserver<ListLogsResponse> r
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListLogs, expected %s or %s",
+                  response.getClass().getName(),
+                  ListLogsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/logging/MockMetricsServiceV2Impl.java b/test/integration/goldens/logging/MockMetricsServiceV2Impl.java
index 4938e889ae..64855c0a62 100644
--- a/test/integration/goldens/logging/MockMetricsServiceV2Impl.java
+++ b/test/integration/goldens/logging/MockMetricsServiceV2Impl.java
@@ -77,7 +77,13 @@ public void listLogMetrics(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListLogMetrics, expected %s or %s",
+                  response.getClass().getName(),
+                  ListLogMetricsResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -92,7 +98,13 @@ public void getLogMetric(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetLogMetric, expected %s or %s",
+                  response.getClass().getName(),
+                  LogMetric.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -107,7 +119,13 @@ public void createLogMetric(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateLogMetric, expected %s or %s",
+                  response.getClass().getName(),
+                  LogMetric.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -122,7 +140,13 @@ public void updateLogMetric(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateLogMetric, expected %s or %s",
+                  response.getClass().getName(),
+                  LogMetric.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -137,7 +161,13 @@ public void deleteLogMetric(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteLogMetric, expected %s or %s",
+                  response.getClass().getName(),
+                  Empty.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }
diff --git a/test/integration/goldens/redis/MockCloudRedisImpl.java b/test/integration/goldens/redis/MockCloudRedisImpl.java
index 953045dea1..bc4e3d8d7d 100644
--- a/test/integration/goldens/redis/MockCloudRedisImpl.java
+++ b/test/integration/goldens/redis/MockCloudRedisImpl.java
@@ -70,7 +70,13 @@ public void listInstances(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ListInstances, expected %s or %s",
+                  response.getClass().getName(),
+                  ListInstancesResponse.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -84,7 +90,13 @@ public void getInstance(GetInstanceRequest request, StreamObserver<Instance> res
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method GetInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Instance.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -99,7 +111,13 @@ public void createInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method CreateInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -114,7 +132,13 @@ public void updateInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpdateInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -129,7 +153,13 @@ public void upgradeInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method UpgradeInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -144,7 +174,13 @@ public void importInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ImportInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -159,7 +195,13 @@ public void exportInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method ExportInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -174,7 +216,13 @@ public void failoverInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method FailoverInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 
@@ -189,7 +237,13 @@ public void deleteInstance(
     } else if (response instanceof Exception) {
       responseObserver.onError(((Exception) response));
     } else {
-      responseObserver.onError(new IllegalArgumentException("Unrecognized response type"));
+      responseObserver.onError(
+          new IllegalArgumentException(
+              String.format(
+                  "Unrecognized response type %s for method DeleteInstance, expected %s or %s",
+                  response.getClass().getName(),
+                  Operation.class.getName(),
+                  Exception.class.getName())));
     }
   }
 }