diff --git a/codegen-server-test/model/pokemon.smithy b/codegen-server-test/model/pokemon.smithy
index 6d4ead7eee9..72469895afd 100644
--- a/codegen-server-test/model/pokemon.smithy
+++ b/codegen-server-test/model/pokemon.smithy
@@ -27,7 +27,7 @@ resource PokemonSpecies {
 operation CapturePokemonOperation {
     input: CapturePokemonOperationEventsInput,
     output: CapturePokemonOperationEventsOutput,
-    errors: [UnsupportedRegionError]
+    errors: [UnsupportedRegionError, MasterBallUnsuccessful]
 }
 
 @input
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerCombinedErrorGenerator.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerCombinedErrorGenerator.kt
index 7af59162e68..58dbfa481b1 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerCombinedErrorGenerator.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerCombinedErrorGenerator.kt
@@ -22,7 +22,7 @@ import software.amazon.smithy.rust.codegen.smithy.generators.CodegenTarget
 import software.amazon.smithy.rust.codegen.smithy.generators.error.errorSymbol
 import software.amazon.smithy.rust.codegen.smithy.generators.error.eventStreamErrorSymbol
 import software.amazon.smithy.rust.codegen.smithy.transformers.getStreamErrors
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 import software.amazon.smithy.rust.codegen.util.isEventStream
 import software.amazon.smithy.rust.codegen.util.toSnakeCase
 
@@ -36,7 +36,7 @@ open class ServerCombinedErrorGenerator(
     private val operation: OperationShape
 ) {
     fun render(writer: RustWriter) {
-        val errors = operation.nonEventStreamErrors(model)
+        val errors = operation.operationErrors(model)
         val symbol = operation.errorSymbol(symbolProvider)
         if (errors.isNotEmpty()) {
             renderErrors(writer, errors.map { it.asStructureShape().get() }, symbol)
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationHandlerGenerator.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationHandlerGenerator.kt
index 320f8a41630..89d49df9cb3 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationHandlerGenerator.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationHandlerGenerator.kt
@@ -17,7 +17,7 @@ import software.amazon.smithy.rust.codegen.server.smithy.protocols.ServerHttpBou
 import software.amazon.smithy.rust.codegen.smithy.CodegenContext
 import software.amazon.smithy.rust.codegen.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.smithy.generators.error.errorSymbol
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 import software.amazon.smithy.rust.codegen.util.hasStreamingMember
 import software.amazon.smithy.rust.codegen.util.inputShape
 import software.amazon.smithy.rust.codegen.util.outputShape
@@ -140,7 +140,7 @@ open class ServerOperationHandlerGenerator(
         } else {
             "Fun: FnOnce($inputName) -> Fut + Clone + Send + 'static,"
         }
-        val outputType = if (operation.nonEventStreamErrors(model).isNotEmpty()) {
+        val outputType = if (operation.operationErrors(model).isNotEmpty()) {
             "Result<${symbolProvider.toSymbol(operation.outputShape(model)).fullName}, ${operation.errorSymbol(symbolProvider).fullyQualifiedName()}>"
         } else {
             symbolProvider.toSymbol(operation.outputShape(model)).fullName
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
index 8499eab2245..514d0485171 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
@@ -59,7 +59,7 @@ import software.amazon.smithy.rust.codegen.smithy.protocols.HttpLocation
 import software.amazon.smithy.rust.codegen.smithy.protocols.Protocol
 import software.amazon.smithy.rust.codegen.smithy.protocols.parse.StructuredDataParserGenerator
 import software.amazon.smithy.rust.codegen.smithy.toOptional
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 import software.amazon.smithy.rust.codegen.smithy.wrapOptional
 import software.amazon.smithy.rust.codegen.util.dq
 import software.amazon.smithy.rust.codegen.util.expectTrait
@@ -218,7 +218,7 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
         val outputName = "${operationName}${ServerHttpBoundProtocolGenerator.OPERATION_OUTPUT_WRAPPER_SUFFIX}"
         val errorSymbol = operationShape.errorSymbol(symbolProvider)
 
-        if (operationShape.nonEventStreamErrors(model).isNotEmpty()) {
+        if (operationShape.operationErrors(model).isNotEmpty()) {
             // The output of fallible operations is a `Result` which we convert into an
             // isomorphic `enum` type we control that can in turn be converted into a response.
             val intoResponseImpl =
@@ -304,7 +304,7 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
         }
 
         // Implement conversion function to "wrap" from the model operation output types.
-        if (operationShape.nonEventStreamErrors(model).isNotEmpty()) {
+        if (operationShape.operationErrors(model).isNotEmpty()) {
             rustTemplate(
                 """
                 impl #{From}<Result<#{O}, #{E}>> for $outputName {
@@ -443,7 +443,7 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
         val operationName = symbolProvider.toSymbol(operationShape).name
         val structuredDataSerializer = protocol.structuredDataSerializer(operationShape)
         withBlock("match error {", "}") {
-            val errors = operationShape.nonEventStreamErrors(model)
+            val errors = operationShape.operationErrors(model)
             errors.forEach {
                 val variantShape = model.expectShape(it.id, StructureShape::class.java)
                 val errorTrait = variantShape.expectTrait<ErrorTrait>()
diff --git a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/CombinedErrorGenerator.kt b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/CombinedErrorGenerator.kt
index 5b3c78e60f6..d9ac691d22b 100644
--- a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/CombinedErrorGenerator.kt
+++ b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/CombinedErrorGenerator.kt
@@ -27,7 +27,7 @@ import software.amazon.smithy.rust.codegen.smithy.RustSymbolProvider
 import software.amazon.smithy.rust.codegen.smithy.customize.Section
 import software.amazon.smithy.rust.codegen.smithy.generators.CodegenTarget
 import software.amazon.smithy.rust.codegen.smithy.transformers.getStreamErrors
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 import software.amazon.smithy.rust.codegen.util.hasTrait
 import software.amazon.smithy.rust.codegen.util.isEventStream
 import software.amazon.smithy.rust.codegen.util.toSnakeCase
@@ -68,7 +68,7 @@ class CombinedErrorGenerator(
 
     fun render(writer: RustWriter) {
         val symbol = operation.errorSymbol(symbolProvider)
-        renderErrors(writer, operation.nonEventStreamErrors(model).map { it.asStructureShape().get() }.toMutableList(), symbol)
+        renderErrors(writer, operation.operationErrors(model).map { it.asStructureShape().get() }.toMutableList(), symbol)
 
         if (operation.isEventStream(model)) {
             val clientErrors = operation.getStreamErrors(model, CodegenTarget.CLIENT).map { it.asStructureShape().get() }
diff --git a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/TopLevelErrorGenerator.kt b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/TopLevelErrorGenerator.kt
index abaf650bc05..0ae3cce3e66 100644
--- a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/TopLevelErrorGenerator.kt
+++ b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/error/TopLevelErrorGenerator.kt
@@ -25,7 +25,7 @@ import software.amazon.smithy.rust.codegen.smithy.RustCrate
 import software.amazon.smithy.rust.codegen.smithy.generators.CodegenTarget
 import software.amazon.smithy.rust.codegen.smithy.transformers.allErrors
 import software.amazon.smithy.rust.codegen.smithy.transformers.getStreamErrors
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 
 /**
  * Each service defines its own "top-level" error combining all possible errors that a service can emit.
@@ -78,7 +78,7 @@ class TopLevelErrorGenerator(codegenContext: CodegenContext, private val operati
     }
 
     private fun RustWriter.renderImplFrom(operationShape: OperationShape) {
-        val nonEventStreamErrors = operationShape.nonEventStreamErrors(model).map { it.id }
+        val nonEventStreamErrors = operationShape.operationErrors(model).map { it.id }
         val allErrors: List<Pair<RuntimeType, List<ShapeId>>> = listOf(
             Pair(operationShape.errorSymbol(symbolProvider), nonEventStreamErrors),
             Pair(
diff --git a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/protocols/HttpBoundProtocolGenerator.kt b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/protocols/HttpBoundProtocolGenerator.kt
index 858ecdf0d95..6fb2e960e00 100644
--- a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/protocols/HttpBoundProtocolGenerator.kt
+++ b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/protocols/HttpBoundProtocolGenerator.kt
@@ -32,7 +32,7 @@ import software.amazon.smithy.rust.codegen.smithy.generators.protocol.ProtocolTr
 import software.amazon.smithy.rust.codegen.smithy.generators.setterName
 import software.amazon.smithy.rust.codegen.smithy.protocols.parse.StructuredDataParserGenerator
 import software.amazon.smithy.rust.codegen.smithy.transformers.errorMessageMember
-import software.amazon.smithy.rust.codegen.smithy.transformers.nonEventStreamErrors
+import software.amazon.smithy.rust.codegen.smithy.transformers.operationErrors
 import software.amazon.smithy.rust.codegen.util.UNREACHABLE
 import software.amazon.smithy.rust.codegen.util.dq
 import software.amazon.smithy.rust.codegen.util.hasStreamingMember
@@ -168,7 +168,7 @@ class HttpBoundProtocolTraitImplGenerator(
                     protocol.parseHttpGenericError(operationShape),
                     errorSymbol
                 )
-                if (operationShape.nonEventStreamErrors(model).isNotEmpty()) {
+                if (operationShape.operationErrors(model).isNotEmpty()) {
                     rustTemplate(
                         """
                         let error_code = match generic.code() {
@@ -181,7 +181,7 @@ class HttpBoundProtocolTraitImplGenerator(
                         "error_symbol" to errorSymbol,
                     )
                     withBlock("Err(match error_code {", "})") {
-                        val errors = operationShape.nonEventStreamErrors(model)
+                        val errors = operationShape.operationErrors(model)
                         errors.forEach { error ->
                             val errorShape = model.expectShape(error.id, StructureShape::class.java)
                             val variantName = symbolProvider.toSymbol(model.expectShape(error.id)).name
diff --git a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/transformers/EventStreamNormalizer.kt b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/transformers/EventStreamNormalizer.kt
index eb22d8fe7d7..6432ca82101 100644
--- a/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/transformers/EventStreamNormalizer.kt
+++ b/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/transformers/EventStreamNormalizer.kt
@@ -7,10 +7,13 @@ package software.amazon.smithy.rust.codegen.smithy.transformers
 
 import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.knowledge.OperationIndex
+import software.amazon.smithy.model.node.Node
 import software.amazon.smithy.model.shapes.OperationShape
 import software.amazon.smithy.model.shapes.Shape
 import software.amazon.smithy.model.shapes.ShapeId
+import software.amazon.smithy.model.shapes.StructureShape
 import software.amazon.smithy.model.shapes.UnionShape
+import software.amazon.smithy.model.traits.AnnotationTrait
 import software.amazon.smithy.model.traits.ErrorTrait
 import software.amazon.smithy.model.transform.ModelTransformer
 import software.amazon.smithy.rust.codegen.smithy.generators.CodegenTarget
@@ -26,10 +29,18 @@ import software.amazon.smithy.rust.codegen.util.isEventStream
  */
 object EventStreamNormalizer {
     fun transform(model: Model): Model = ModelTransformer.create().mapShapes(model) { shape ->
-        if (shape is OperationShape && shape.isEventStream(model)) {
-            addStreamErrorsToOperationErrors(model, shape)
+        if (shape is OperationShape) {
+            val newErrors = shape.errors
+                .map { model.expectShape(it, StructureShape::class.java) }
+                .map { it.toBuilder().addTrait(SyntheticOperationErrorTrait()).build() }
+            val newShape = shape.toBuilder().errors(newErrors.map { it.id }).build()
+            if (newShape.isEventStream(model)) {
+                addStreamErrorsToOperationErrors(model, newShape)
+            } else {
+                newShape
+            }
         } else if (shape is UnionShape && shape.isEventStream()) {
-            syntheticEquivalent(model, shape)
+            syntheticEquivalentEventStreamUnion(model, shape)
         } else {
             shape
         }
@@ -54,7 +65,7 @@ object EventStreamNormalizer {
             .build()
     }
 
-    private fun syntheticEquivalent(model: Model, union: UnionShape): UnionShape {
+    private fun syntheticEquivalentEventStreamUnion(model: Model, union: UnionShape): UnionShape {
         val (errorMembers, eventMembers) = union.members().partition { member ->
             model.expectShape(member.target).hasTrait<ErrorTrait>()
         }
@@ -82,14 +93,20 @@ fun OperationShape.getStreamErrors(model: Model, target: CodegenTarget): List<Sh
         CodegenTarget.SERVER -> inputOutput.filter { it.expectTrait<ErrorTrait>().isClientError }
     }
 }
-fun OperationShape.nonEventStreamErrors(model: Model): List<Shape> {
+fun OperationShape.operationErrors(model: Model): List<Shape> {
     val operationIndex = OperationIndex.of(model)
-    val eventStreamErrors = this.eventStreamErrors(model)
-    return operationIndex.getErrors(this).filter { !eventStreamErrors.contains(it) }
+    return operationIndex.getErrors(this)
+        .filter { it.hasTrait<SyntheticOperationErrorTrait>() }
 }
 fun OperationShape.eventStreamErrors(model: Model): List<Shape> {
     return this.getStreamErrors(model, CodegenTarget.CLIENT) + this.getStreamErrors(model, CodegenTarget.SERVER)
 }
 fun OperationShape.allErrors(model: Model): List<Shape> {
-    return this.eventStreamErrors(model) + this.nonEventStreamErrors(model)
+    return this.eventStreamErrors(model) + this.operationErrors(model)
+}
+
+class SyntheticOperationErrorTrait : AnnotationTrait(ID, Node.objectNode()) {
+    companion object {
+        val ID = ShapeId.from("smithy.api.internal#syntheticOperationErrorTrait")
+    }
 }