diff --git a/test/unit/legacy-noattributes.html b/test/unit/legacy-noattributes.html
index 10072b5d7c..92ed94d828 100644
--- a/test/unit/legacy-noattributes.html
+++ b/test/unit/legacy-noattributes.html
@@ -118,6 +118,7 @@
       });
 
       test('native properties observeable when `_legacyForceObservedAttributes` set', function() {
+        // Unsupported when polyfill is in use since it uses `setAttribute`.
         if (customElements.polyfillWrapFlushCallback) {
           this.skip();
         }