diff --git a/externs/closure-types.js b/externs/closure-types.js
index eadc31f64a..c420bc296b 100644
--- a/externs/closure-types.js
+++ b/externs/closure-types.js
@@ -210,9 +210,10 @@ Polymer_PropertyEffects.prototype._setPendingPropertyOrPath = function(path, val
 Polymer_PropertyEffects.prototype._setUnmanagedPropertyToNode = function(node, prop, value){};
 /**
 * @override
-* @param {*} property
+* @param {string} property
 * @param {*} value
-* @param {*} shouldNotify
+* @param {boolean=} shouldNotify
+* @return {boolean}
 */
 Polymer_PropertyEffects.prototype._setPendingProperty = function(property, value, shouldNotify){};
 /**
diff --git a/gulpfile.js b/gulpfile.js
index a2cfef0b61..789ea7ad1b 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -96,7 +96,7 @@ let EXPECTED_WARNING_COUNT = 498;
 
 gulp.task('clean', () => del(DIST_DIR));
 
-gulp.task('closure', ['clean'], () => {
+gulp.task('closure', ['clean', 'generate-closure-externs'], () => {
 
   let entry, splitRx, joinRx;
 
@@ -242,3 +242,10 @@ gulp.task('lint', function() {
     .pipe(eslint.format())
     .pipe(eslint.failAfterError());
 });
+
+gulp.task('generate-closure-externs', ['clean'], () => {
+  let genClosure = require('@polymer/gen-closure-declarations').generateDeclarations;
+  return genClosure().then((declarations) => {
+    fs.writeFileSync('externs/closure-types.js', declarations);
+  });
+});
\ No newline at end of file
diff --git a/package.json b/package.json
index d9e3423390..a41ca8b1cb 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "test": "test"
   },
   "devDependencies": {
+    "@polymer/gen-closure-declarations": "0.0.3",
     "babel-preset-babili": "0.0.12",
     "del": "^2.2.1",
     "dom5": "^1.3.1",