diff --git a/CHANGELOG.md b/CHANGELOG.md
index 54839e0afb..f505467079 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ Gaps between patch versions are faulty/broken releases.
 ## 2.2.0
 
  * Make `system` module formatter modules anonymous by default.
+ * Fix duplicate comments being output, breaking code.
 
 ## 2.1.0
 
diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index dd839faa23..4745caedad 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -293,8 +293,9 @@ t.removeComments = function (child) {
 };
 
 t.inheritsComments = function (child, parent) {
-  child.leadingComments  = _.compact([].concat(child.leadingComments, parent.leadingComments));
-  child.trailingComments = _.compact([].concat(child.trailingComments, parent.trailingComments));
+  _.each(["leadingComments", "trailingComments"], function (key) {
+    child[key]  = _.uniq(_.compact([].concat(child[key], parent[key])));
+  });
   return child;
 };