diff --git a/tubular/scripts/dd_synthetic_tests.py b/tubular/scripts/dd_synthetic_tests.py
index 59cda883..c29c4ce0 100644
--- a/tubular/scripts/dd_synthetic_tests.py
+++ b/tubular/scripts/dd_synthetic_tests.py
@@ -63,7 +63,7 @@ def get_failed_tests(self, test_requests):
         for test in test_requests:
             test_result = self._poll_for_test_result(test['id'])
             if test_result == False:
-                failed_tests.add(test)
+                failed_tests.append(test)
 
         return failed_tests