diff --git a/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java b/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
index 051aff1b83..6782d645f3 100644
--- a/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
+++ b/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
@@ -87,6 +87,9 @@ public class Parser {
           "google.iam.v1.IAMPolicy",
           "google.longrunning.Operations",
           "google.cloud.location.Locations");
+  // These must be kept in sync with the above protos' java_package options.
+  private static final Set<String> MIXIN_JAVA_PACKAGE_ALLOWLIST =
+      ImmutableSet.of("com.google.iam.v1", "com.google.longrunning", "com.google.cloud.location");
 
   // Allow other parsers to access this.
   protected static final SourceCodeInfoParser SOURCE_CODE_INFO_PARSER = new SourceCodeInfoParser();
@@ -574,7 +577,7 @@ public static Map<String, Message> updateResourceNamesInMessages(
   }
 
   public static Map<String, ResourceName> parseResourceNames(CodeGeneratorRequest request) {
-    @VisibleForTesting String javaPackage = parseServiceJavaPackage(request);
+    String javaPackage = parseServiceJavaPackage(request);
     Map<String, FileDescriptor> fileDescriptors = getFilesToGenerate(request);
     Map<String, ResourceName> resourceNames = new HashMap<>();
     for (String fileToGenerate : request.getFileToGenerateList()) {
@@ -917,8 +920,23 @@ private static String parseServiceJavaPackage(CodeGeneratorRequest request) {
       }
     }
 
+    // Filter out mixin packages.
+    Map<String, Integer> processedJavaPackageCount =
+        javaPackageCount.entrySet().stream()
+            .filter(e -> !MIXIN_JAVA_PACKAGE_ALLOWLIST.contains(e.getKey()))
+            .collect(Collectors.toMap(e -> e.getKey(), e -> e.getValue()));
+
+    // An empty map indicates that only mixin packages were present, which means that we're
+    // generating a standalone client for a mixin.
+    if (processedJavaPackageCount.isEmpty()) {
+      processedJavaPackageCount = javaPackageCount;
+    }
+
     String finalJavaPackage =
-        javaPackageCount.entrySet().stream().max(Map.Entry.comparingByValue()).get().getKey();
+        processedJavaPackageCount.entrySet().stream()
+            .max(Map.Entry.comparingByValue())
+            .get()
+            .getKey();
     Preconditions.checkState(
         !Strings.isNullOrEmpty(finalJavaPackage), "No service Java package found");
     return finalJavaPackage;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClient.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClient.java
index 13acfd990c..66ecc5c548 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClient.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClient.java
@@ -31,7 +31,6 @@
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -41,6 +40,7 @@
 import com.google.pubsub.v1.GetSchemaRequest;
 import com.google.pubsub.v1.ListSchemasRequest;
 import com.google.pubsub.v1.ListSchemasResponse;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.Schema;
 import com.google.pubsub.v1.SchemaName;
 import com.google.pubsub.v1.ValidateMessageRequest;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClientTest.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClientTest.java
index 78e5913bab..ace5e7d42b 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClientTest.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SchemaServiceClientTest.java
@@ -30,7 +30,6 @@
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.GetPolicyOptions;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -43,6 +42,7 @@
 import com.google.pubsub.v1.GetSchemaRequest;
 import com.google.pubsub.v1.ListSchemasRequest;
 import com.google.pubsub.v1.ListSchemasResponse;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.Schema;
 import com.google.pubsub.v1.SchemaName;
 import com.google.pubsub.v1.ValidateMessageRequest;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClient.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClient.java
index c7d77041cb..3ed9e66388 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClient.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClient.java
@@ -32,7 +32,6 @@
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -49,6 +48,7 @@
 import com.google.pubsub.v1.ListSubscriptionsResponse;
 import com.google.pubsub.v1.ModifyAckDeadlineRequest;
 import com.google.pubsub.v1.ModifyPushConfigRequest;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.PullRequest;
 import com.google.pubsub.v1.PullResponse;
 import com.google.pubsub.v1.PushConfig;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClientTest.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClientTest.java
index 70b562af07..0b89cc59e1 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClientTest.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/SubscriptionAdminClientTest.java
@@ -35,7 +35,6 @@
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.GetPolicyOptions;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -59,6 +58,7 @@
 import com.google.pubsub.v1.ListSubscriptionsResponse;
 import com.google.pubsub.v1.ModifyAckDeadlineRequest;
 import com.google.pubsub.v1.ModifyPushConfigRequest;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.PullRequest;
 import com.google.pubsub.v1.PullResponse;
 import com.google.pubsub.v1.PushConfig;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClient.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClient.java
index 21cafd6f67..48d61edc58 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClient.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClient.java
@@ -31,7 +31,6 @@
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -46,6 +45,7 @@
 import com.google.pubsub.v1.ListTopicSubscriptionsResponse;
 import com.google.pubsub.v1.ListTopicsRequest;
 import com.google.pubsub.v1.ListTopicsResponse;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.PublishRequest;
 import com.google.pubsub.v1.PublishResponse;
 import com.google.pubsub.v1.PubsubMessage;
diff --git a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClientTest.java b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClientTest.java
index 11623b3614..09b8de0f90 100644
--- a/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClientTest.java
+++ b/test/integration/goldens/pubsub/com/google/cloud/pubsub/v1/TopicAdminClientTest.java
@@ -32,7 +32,6 @@
 import com.google.iam.v1.GetIamPolicyRequest;
 import com.google.iam.v1.GetPolicyOptions;
 import com.google.iam.v1.Policy;
-import com.google.iam.v1.ProjectName;
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
@@ -51,6 +50,7 @@
 import com.google.pubsub.v1.ListTopicsRequest;
 import com.google.pubsub.v1.ListTopicsResponse;
 import com.google.pubsub.v1.MessageStoragePolicy;
+import com.google.pubsub.v1.ProjectName;
 import com.google.pubsub.v1.PublishRequest;
 import com.google.pubsub.v1.PublishResponse;
 import com.google.pubsub.v1.PubsubMessage;
diff --git a/test/integration/goldens/pubsub/com/google/iam/v1/ProjectName.java b/test/integration/goldens/pubsub/com/google/pubsub/v1/ProjectName.java
similarity index 99%
rename from test/integration/goldens/pubsub/com/google/iam/v1/ProjectName.java
rename to test/integration/goldens/pubsub/com/google/pubsub/v1/ProjectName.java
index 21108a2658..f95b105766 100644
--- a/test/integration/goldens/pubsub/com/google/iam/v1/ProjectName.java
+++ b/test/integration/goldens/pubsub/com/google/pubsub/v1/ProjectName.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.google.iam.v1;
+package com.google.pubsub.v1;
 
 import com.google.api.pathtemplate.PathTemplate;
 import com.google.api.resourcenames.ResourceName;