diff --git a/src/lib/style-extends.html b/src/lib/style-extends.html
index 0f0e41ee4a..93b2fe625c 100644
--- a/src/lib/style-extends.html
+++ b/src/lib/style-extends.html
@@ -67,7 +67,7 @@
       if (target.parent !== source.parent) {
         this._cloneAndAddRuleToParent(source, target.parent);
       }
-      target.extends = target.extends || (target.extends = []);
+      target.extends = target.extends || [];
       target.extends.push(source);
       // TODO: this misses `%foo, .bar` as an unetended selector but
       // this seems rare and could possibly be unsupported.