diff --git a/tests/s3_tester.c b/tests/s3_tester.c
index ca8d5f45e..0070228b3 100644
--- a/tests/s3_tester.c
+++ b/tests/s3_tester.c
@@ -1766,7 +1766,9 @@ int aws_s3_tester_send_meta_request_with_options(
             aws_s3_tester_wait_for_meta_request_shutdown(tester);
         }
     } else {
-        ASSERT_INT_EQUALS(0,tester->synced_data.meta_request_shutdown_count);
+        aws_s3_tester_lock_synced_data(tester);
+        ASSERT_INT_EQUALS(0, tester->synced_data.meta_request_shutdown_count);
+        aws_s3_tester_unlock_synced_data(tester);
     }
 
     aws_s3_meta_request_test_results_clean_up(&meta_request_test_results);