diff --git a/testing/web-platform/tests/tools/wptrunner/wptrunner/testloader.py b/testing/web-platform/tests/tools/wptrunner/wptrunner/testloader.py
index 889b2df03201..8758887d20a0 100644
--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/testloader.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/testloader.py
@@ -376,7 +376,7 @@ class SingleTestSource(TestSource):
 
     @classmethod
     def tests_by_group(cls, tests, **kwargs):
-        return {cls.group_metadata(None): [t.id for t in tests]}
+        return {cls.group_metadata(None)['scope']: [t.id for t in tests]}
 
 
 class PathGroupedSource(GroupedSource):