diff --git a/externs/closure-types.js b/externs/closure-types.js
index c8b38c77e3..e97a702165 100644
--- a/externs/closure-types.js
+++ b/externs/closure-types.js
@@ -105,9 +105,10 @@ Polymer_PropertiesChanged.prototype._shouldPropertyChange = function(property, v
 * @param {string} name Name of attribute that changed
 * @param {?string} old Old attribute value
 * @param {?string} value New attribute value
+* @param {?string} namespace Attribute namespace.
 * @return {void}
 */
-Polymer_PropertiesChanged.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_PropertiesChanged.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @param {string} attribute Name of attribute to deserialize.
 * @param {?string} value of the attribute.
@@ -972,9 +973,10 @@ Polymer_LegacyElementMixin.prototype._initializeProperties = function(){};
 * @param {string} name Name of attribute.
 * @param {?string} old Old value of attribute.
 * @param {?string} value Current value of attribute.
+* @param {?string} namespace Attribute namespace.
 * @return {void}
 */
-Polymer_LegacyElementMixin.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_LegacyElementMixin.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @override
 * @return {void}
@@ -1391,7 +1393,7 @@ Polymer_DisableUpgradeMixin.prototype._enableProperties = function(){};
 /**
 * @override
 */
-Polymer_DisableUpgradeMixin.prototype.attributeChangedCallback = function(name, old, value){};
+Polymer_DisableUpgradeMixin.prototype.attributeChangedCallback = function(name, old, value, namespace){};
 /**
 * @override
 */
diff --git a/types/lib/elements/dom-module.d.ts b/types/lib/elements/dom-module.d.ts
index 7229968d42..e745986b7f 100644
--- a/types/lib/elements/dom-module.d.ts
+++ b/types/lib/elements/dom-module.d.ts
@@ -63,8 +63,9 @@ declare namespace Polymer {
      * @param name Name of attribute.
      * @param old Old value of attribute.
      * @param value Current value of attribute.
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Registers the dom-module at a given id. This method should only be called
diff --git a/types/lib/legacy/legacy-element-mixin.d.ts b/types/lib/legacy/legacy-element-mixin.d.ts
index cfe9164678..e28fd84f68 100644
--- a/types/lib/legacy/legacy-element-mixin.d.ts
+++ b/types/lib/legacy/legacy-element-mixin.d.ts
@@ -63,8 +63,9 @@ declare namespace Polymer {
      * @param name Name of attribute.
      * @param old Old value of attribute.
      * @param value Current value of attribute.
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Provides an implementation of `connectedCallback`
diff --git a/types/lib/mixins/disable-upgrade-mixin.d.ts b/types/lib/mixins/disable-upgrade-mixin.d.ts
index f8584219d8..858b4a1e7d 100644
--- a/types/lib/mixins/disable-upgrade-mixin.d.ts
+++ b/types/lib/mixins/disable-upgrade-mixin.d.ts
@@ -42,7 +42,7 @@ declare namespace Polymer {
   interface DisableUpgradeMixin {
     _initializeProperties(): void;
     _enableProperties(): void;
-    attributeChangedCallback(name: any, old: any, value: any): void;
+    attributeChangedCallback(name: any, old: any, value: any, namespace: any): void;
     connectedCallback(): void;
     disconnectedCallback(): void;
   }
diff --git a/types/lib/mixins/properties-changed.d.ts b/types/lib/mixins/properties-changed.d.ts
index 13364e1980..0c074275bd 100644
--- a/types/lib/mixins/properties-changed.d.ts
+++ b/types/lib/mixins/properties-changed.d.ts
@@ -235,8 +235,9 @@ declare namespace Polymer {
      * @param name Name of attribute that changed
      * @param old Old attribute value
      * @param value New attribute value
+     * @param namespace Attribute namespace.
      */
-    attributeChangedCallback(name: string, old: string|null, value: string|null): void;
+    attributeChangedCallback(name: string, old: string|null, value: string|null, namespace: string|null): void;
 
     /**
      * Deserializes an attribute to its associated property.