diff --git a/client-runtime/src/main/java/com/microsoft/rest/UserAgentInterceptor.java b/client-runtime/src/main/java/com/microsoft/rest/UserAgentInterceptor.java
index bb15c0f4305de..7705592ba9f72 100644
--- a/client-runtime/src/main/java/com/microsoft/rest/UserAgentInterceptor.java
+++ b/client-runtime/src/main/java/com/microsoft/rest/UserAgentInterceptor.java
@@ -47,11 +47,19 @@ public void appendUserAgent(String userAgent) {
     public Response intercept(Chain chain) throws IOException {
         Request request = chain.request();
         String header = request.header("User-Agent");
-        if (header == null || !userAgent.equals(DEFAULT_USER_AGENT_HEADER)) {
-            request = chain.request().newBuilder()
-                    .header("User-Agent", userAgent + " " + header)
-                    .build();
+        if (header == null) {
+            header = DEFAULT_USER_AGENT_HEADER;
         }
+        if (!userAgent.equals(DEFAULT_USER_AGENT_HEADER)) {
+            if (header.equals(DEFAULT_USER_AGENT_HEADER)) {
+                header = userAgent;
+            } else {
+                header = userAgent + " " + header;
+            }
+        }
+        request = chain.request().newBuilder()
+                .header("User-Agent", header)
+                .build();
         return chain.proceed(request);
     }
 }
diff --git a/client-runtime/src/test/java/com/microsoft/rest/CredentialsTests.java b/client-runtime/src/test/java/com/microsoft/rest/CredentialsTests.java
index 19b7a8ca2a4f5..9071c9ae9dc4f 100644
--- a/client-runtime/src/test/java/com/microsoft/rest/CredentialsTests.java
+++ b/client-runtime/src/test/java/com/microsoft/rest/CredentialsTests.java
@@ -9,19 +9,14 @@
 
 import com.microsoft.rest.credentials.BasicAuthenticationCredentials;
 import com.microsoft.rest.credentials.TokenCredentials;
-
+import com.microsoft.rest.serializer.JacksonMapperAdapter;
+import okhttp3.*;
 import org.junit.Assert;
 import org.junit.Test;
+import retrofit2.Retrofit;
 
 import java.io.IOException;
 
-import okhttp3.Interceptor;
-import okhttp3.OkHttpClient;
-import okhttp3.Protocol;
-import okhttp3.Request;
-import okhttp3.Response;
-import retrofit2.Retrofit;
-
 public class CredentialsTests {
     @Test
     public void basicCredentialsTest() throws Exception {
@@ -29,6 +24,7 @@ public void basicCredentialsTest() throws Exception {
         Retrofit.Builder retrofitBuilder = new Retrofit.Builder();
         BasicAuthenticationCredentials credentials = new BasicAuthenticationCredentials("user", "pass");
         RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder)
+                .withMapperAdapter(new JacksonMapperAdapter())
                 .withCredentials(credentials)
                 .withInterceptor(new Interceptor() {
             @Override
@@ -53,6 +49,7 @@ public void tokenCredentialsTest() throws Exception {
         Retrofit.Builder retrofitBuilder = new Retrofit.Builder();
         TokenCredentials credentials = new TokenCredentials(null, "this_is_a_token");
         RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder)
+                .withMapperAdapter(new JacksonMapperAdapter())
                 .withCredentials(credentials)
                 .withInterceptor(new Interceptor() {
                     @Override
diff --git a/client-runtime/src/test/java/com/microsoft/rest/RetryHandlerTests.java b/client-runtime/src/test/java/com/microsoft/rest/RetryHandlerTests.java
index 050e7374aba18..97c46f6fe4fc3 100644
--- a/client-runtime/src/test/java/com/microsoft/rest/RetryHandlerTests.java
+++ b/client-runtime/src/test/java/com/microsoft/rest/RetryHandlerTests.java
@@ -9,6 +9,7 @@
 
 import com.microsoft.rest.retry.RetryHandler;
 
+import com.microsoft.rest.serializer.JacksonMapperAdapter;
 import okhttp3.Interceptor;
 import okhttp3.OkHttpClient;
 import okhttp3.Protocol;
@@ -41,7 +42,8 @@ public Response intercept(Chain chain) throws IOException {
                         .build();
             }
         });
-        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder);
+        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder)
+                .withMapperAdapter(new JacksonMapperAdapter());
         ServiceClient serviceClient = new ServiceClient(restBuilder.build()) { };
         Response response = serviceClient.restClient().httpClient().newCall(
                 new Request.Builder().url("http://localhost").get().build()).execute();
@@ -67,7 +69,8 @@ public Response intercept(Chain chain) throws IOException {
                         .build();
             }
         });
-        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder);
+        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder)
+                .withMapperAdapter(new JacksonMapperAdapter());
         ServiceClient serviceClient = new ServiceClient(restBuilder.build()) { };
         Response response = serviceClient.restClient().httpClient().newCall(
                 new Request.Builder().url("http://localhost").get().build()).execute();
diff --git a/client-runtime/src/test/java/com/microsoft/rest/ServiceClientTests.java b/client-runtime/src/test/java/com/microsoft/rest/ServiceClientTests.java
index 5497d607549d7..de57b15dc397d 100644
--- a/client-runtime/src/test/java/com/microsoft/rest/ServiceClientTests.java
+++ b/client-runtime/src/test/java/com/microsoft/rest/ServiceClientTests.java
@@ -7,18 +7,14 @@
 
 package com.microsoft.rest;
 
+import com.microsoft.rest.serializer.JacksonMapperAdapter;
+import okhttp3.*;
 import org.junit.Assert;
 import org.junit.Test;
+import retrofit2.Retrofit;
 
 import java.io.IOException;
 
-import okhttp3.Interceptor;
-import okhttp3.OkHttpClient;
-import okhttp3.Protocol;
-import okhttp3.Request;
-import okhttp3.Response;
-import retrofit2.Retrofit;
-
 public class ServiceClientTests {
     @Test
     public void filterTests() throws Exception {
@@ -38,7 +34,8 @@ public Response intercept(Chain chain) throws IOException {
                         .build();
             }
         });
-        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder);
+        RestClient.Builder restBuilder = new RestClient.Builder("http://localhost", clientBuilder, retrofitBuilder)
+                .withMapperAdapter(new JacksonMapperAdapter());
         ServiceClient serviceClient = new ServiceClient(restBuilder.build()) { };
         Response response = serviceClient.restClient().httpClient().newCall(new Request.Builder().url("http://localhost").build()).execute();
         Assert.assertEquals(200, response.code());