diff --git a/google/cloud/sql/v1/cloud_sql_instances.proto b/google/cloud/sql/v1/cloud_sql_instances.proto
index ba42b677231be..d80a1367a74be 100644
--- a/google/cloud/sql/v1/cloud_sql_instances.proto
+++ b/google/cloud/sql/v1/cloud_sql_instances.proto
@@ -1611,6 +1611,12 @@ message SqlExternalSyncSettingError {
     // The error message indicates that pg_cron flags are enabled on the
     // destination which is not supported during the migration.
     PG_CRON_FLAG_ENABLED_IN_REPLICA = 47;
+
+    // This error message indicates that the specified extensions are not
+    // enabled on destination instance. For example, before you can migrate
+    // data to the destination instance, you must enable the PGAudit extension
+    // on the instance.
+    EXTENSIONS_NOT_ENABLED_IN_REPLICA = 48;
   }
 
   // Can be `sql#externalSyncSettingError` or