diff --git a/packages/core/src/core.externs.js b/packages/core/src/core.externs.js
index 936424081b516..022c2f74e291d 100644
--- a/packages/core/src/core.externs.js
+++ b/packages/core/src/core.externs.js
@@ -16,3 +16,9 @@
  * @suppress {duplicate}
  */
 var wtf;
+
+/**
+ * This is needed to declare global `$localize` to let closure compiler know
+ * about the global variable.
+ */
+var $localize;