diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index fe0097fc79..5143b9bfba 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -387,8 +387,11 @@ Scope.prototype.parentGet = function (id, decl) {
  */
 
 Scope.prototype.has = function (id, decl) {
-  return (id && (this.hasOwn(id, decl) || this.parentHas(id, decl))) ||
-         contains(Scope.defaultDeclarations, id);
+  if (!id) return false;
+  if (this.hasOwn(id, decl)) return true;
+  if (this.parentHas(id, decl)) return true;
+  if (contains(Scope.defaultDeclarations, id)) return true;
+  return false;
 };
 
 /**