--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -1413,22 +1413,22 @@ class TreeMetadataEmitter(LoggingMixin):
         # Create a equivalent TestManifest object
         obj = TestManifest(context, manifest_full_path, manifest,
                            flavor="web-platform-tests",
                            relpath=mozpath.join(manifest_reldir,
                                                 mozpath.basename(manifest_path)),
                            install_prefix="web-platform/")
 
 
-        for path, tests in manifest:
+        for test_type, path, tests in manifest:
             path = mozpath.join(tests_root, path)
+            if test_type not in ["testharness", "reftest", "wdspec"]:
+                continue
+
             for test in tests:
-                if test.item_type not in ["testharness", "reftest"]:
-                    continue
-
                 obj.tests.append({
                     'path': path,
                     'here': mozpath.dirname(path),
                     'manifest': manifest_path,
                     'name': test.id,
                     'head': '',
                     'tail': '',
                     'support-files': '',