diff --git a/lib/6to5/transformation/transformers/let-scoping.js b/lib/6to5/transformation/transformers/let-scoping.js
index 9ccd879620..7998e9e362 100644
--- a/lib/6to5/transformation/transformers/let-scoping.js
+++ b/lib/6to5/transformation/transformers/let-scoping.js
@@ -128,6 +128,12 @@ LetScoping.prototype.run = function () {
   var call = t.callExpression(fn, params);
   var ret  = t.identifier(this.file.generateUid("ret", this.scope));
 
+  var hasYield = traverse.hasType(fn.body, "YieldExpression", t.FUNCTION_TYPES);
+  if (hasYield) {
+    fn.generator = true;
+    call = t.yieldExpression(call, true);
+  }
+
   this.build(ret, call);
 };
 
@@ -245,28 +251,34 @@ LetScoping.prototype.checkFor = function () {
     hasBreak:    false,
   };
 
-  if (this.forParent) {
-    traverse(this.block, function (node) {
-      var replace;
+  var forParent = this.forParent;
 
-      if (t.isFunction(node) || t.isFor(node)) {
-        return false;
-      } else if (t.isBreakStatement(node) && !node.label) {
+  traverse(this.block, function (node) {
+    var replace;
+
+    if (t.isFunction(node) || t.isFor(node)) {
+      return false;
+    }
+
+    if (forParent && !node.label) {
+      if (t.isBreakStatement(node)) {
         has.hasBreak = true;
         replace = t.returnStatement(t.literal("break"));
-      } else if (t.isContinueStatement(node) && !node.label) {
+      } else if (t.isContinueStatement(node)) {
         has.hasContinue = true;
         replace = t.returnStatement(t.literal("continue"));
-      } else if (t.isReturnStatement(node)) {
-        has.hasReturn = true;
-        replace = t.returnStatement(t.objectExpression([
-          t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
-        ]));
       }
+    }
 
-      if (replace) return t.inherits(replace, node);
-    });
-  }
+    if (t.isReturnStatement(node)) {
+      has.hasReturn = true;
+      replace = t.returnStatement(t.objectExpression([
+        t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
+      ]));
+    }
+
+    if (replace) return t.inherits(replace, node);
+  });
 
   return has;
 };
diff --git a/lib/6to5/types/builder-keys.json b/lib/6to5/types/builder-keys.json
index cf85a639df..79003df3ff 100644
--- a/lib/6to5/types/builder-keys.json
+++ b/lib/6to5/types/builder-keys.json
@@ -21,5 +21,6 @@
   "SequenceExpression":      ["expressions"],
   "UnaryExpression":         ["operator", "argument", "prefix"],
   "VariableDeclaration":     ["kind", "declarations"],
-  "VariableDeclarator":      ["id", "init"]
+  "VariableDeclarator":      ["id", "init"],
+  "YieldExpression":         ["argument", "delegate"]
 }