--- a/python/mozbuild/mozbuild/frontend/reader.py
+++ b/python/mozbuild/mozbuild/frontend/reader.py
@@ -1411,17 +1411,17 @@ class BuildReader(object):
         for ctx in ctxs:
             for key in ctx:
                 if key not in test_manifest_contexts:
                     continue
                 for paths, obj in ctx[key]:
                     if isinstance(paths, tuple):
                         path, tests_root = paths
                         tests_root = mozpath.join(ctx.relsrcdir, tests_root)
-                        for t in (mozpath.join(tests_root, path) for path, _ in obj):
+                        for t in (mozpath.join(tests_root, it[0]) for it in obj):
                             result_context.test_files.add(mozpath.dirname(t) + '/**')
                     else:
                         for t in obj.tests:
                             if isinstance(t, tuple):
                                 path, _ = t
                                 relpath = mozpath.relpath(path,
                                                           self.config.topsrcdir)
                             else: