diff --git a/static/third_party/lib/blockly/core/goog-polyfill.js b/static/third_party/lib/blockly/core/goog-polyfill.js
index cd5c9d1f8..19e4cfe1b 100644
--- a/static/third_party/lib/blockly/core/goog-polyfill.js
+++ b/static/third_party/lib/blockly/core/goog-polyfill.js
@@ -68,4 +68,13 @@ Blockly.goog.isNumber = function(val) {
  */
 Blockly.goog.isFunction = function(val) {
   return typeof val == 'function';
+};
+
+/**
+ * Returns true if the specified value is an array.
+ * @param {?} val Variable to test.
+ * @return {boolean} Whether variable is an array.
+ */
+Blockly.goog.isArray = function(val) {
+  return Array.isArray(val);
 };
\ No newline at end of file