diff --git a/gulpfile.js b/gulpfile.js
index 047db161bc..d4abadcf4f 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -70,6 +70,7 @@ const header =
 `/**
  * @fileoverview Generated typings for Polymer mixins
  * @externs
+ * @suppress {checkPrototypalTypes}
  *
  * @license
  * Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
diff --git a/lib/mixins/dir-mixin.js b/lib/mixins/dir-mixin.js
index bbacb2cdb8..6b458e11a8 100644
--- a/lib/mixins/dir-mixin.js
+++ b/lib/mixins/dir-mixin.js
@@ -1,4 +1,5 @@
 /**
+ * @suppress {checkPrototypalTypes}
 @license
 Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
diff --git a/lib/mixins/disable-upgrade-mixin.js b/lib/mixins/disable-upgrade-mixin.js
index b7f46486e2..7d4d73404f 100644
--- a/lib/mixins/disable-upgrade-mixin.js
+++ b/lib/mixins/disable-upgrade-mixin.js
@@ -1,4 +1,5 @@
 /**
+ * @suppress {checkPrototypalTypes}
 @license
 Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
diff --git a/lib/mixins/element-mixin.js b/lib/mixins/element-mixin.js
index d33653b0d7..5c8d4e0311 100644
--- a/lib/mixins/element-mixin.js
+++ b/lib/mixins/element-mixin.js
@@ -1,4 +1,5 @@
 /**
+ * @suppress {checkPrototypalTypes}
 @license
 Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
diff --git a/lib/mixins/property-effects.js b/lib/mixins/property-effects.js
index ac85472154..c3ae4ed385 100644
--- a/lib/mixins/property-effects.js
+++ b/lib/mixins/property-effects.js
@@ -1,4 +1,5 @@
 /**
+ * @suppress {checkPrototypalTypes}
 @license
 Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt