diff --git a/CHANGELOG.md b/CHANGELOG.md
index f08303111f..5c70812b8f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,11 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 4.2.1
+
+ * **Polish**
+  * Add auxiliary comment to let scoping closure flow control.
+
 ## 4.2.0
 
  * **Polish**
diff --git a/lib/babel/transformation/transformers/es6/block-scoping.js b/lib/babel/transformation/transformers/es6/block-scoping.js
index 9b06f1adac..bf486fb2b1 100644
--- a/lib/babel/transformation/transformers/es6/block-scoping.js
+++ b/lib/babel/transformation/transformers/es6/block-scoping.js
@@ -546,14 +546,16 @@ BlockScoping.prototype.buildHas = function (ret, call) {
 
     if (cases.length === 1) {
       var single = cases[0];
-      body.push(t.ifStatement(
+      body.push(this.file.attachAuxiliaryComment(t.ifStatement(
         t.binaryExpression("===", ret, single.test),
         single.consequent[0]
-      ));
+      )));
     } else {
-      body.push(t.switchStatement(ret, cases));
+      body.push(this.file.attachAuxiliaryComment(t.switchStatement(ret, cases)));
     }
   } else {
-    if (has.hasReturn) body.push(retCheck);
+    if (has.hasReturn) {
+      body.push(this.file.attachAuxiliaryComment(retCheck));
+    }
   }
 };