diff --git a/core/field_registry.js b/core/field_registry.js
index 7f431ff7d..463308d3e 100644
--- a/core/field_registry.js
+++ b/core/field_registry.js
@@ -54,7 +54,7 @@ Blockly.fieldRegistry.unregister = function(type) {
  * @package
  */
 Blockly.fieldRegistry.fromJson = function(options) {
-  var fieldObject = /** @type {?Blockly.IRegistrableField} */ (
+  const fieldObject = /** @type {?Blockly.IRegistrableField} */ (
     Blockly.registry.getObject(Blockly.registry.Type.FIELD, options['type']));
   if (!fieldObject) {
     console.warn('Blockly could not create a field of type ' + options['type'] +