diff --git a/core/modules/system/system.js b/core/modules/system/system.js
index 66fd4f5..09f5528 100644
--- a/core/modules/system/system.js
+++ b/core/modules/system/system.js
@@ -28,18 +28,25 @@ Drupal.hideEmailAdministratorCheckbox = function () {
  */
 Drupal.behaviors.copyFieldValue = {
   attach: function (context, settings) {
-    for (var sourceId in settings.copyFieldValue) {
-      $('#' + sourceId, context).once('copy-field-values').bind('blur', function () {
-        // Get the list of target fields.
-        var targetIds = settings.copyFieldValue[sourceId];
-        // Add the behavior to update target fields on blur of the primary field.
-        for (var delta in targetIds) {
+
+    function blurCopyFieldValueHandler(e) {
+      // Get the list of target fields.
+      var targetIds = settings.copyFieldValue[e.target.id];
+      // Add the behavior to update target fields on blur of the primary field.
+      for (var delta in targetIds) {
+        if (targetIds.hasOwnProperty(delta)) {
           var targetField = $('#' + targetIds[delta]);
           if (targetField.val() === '') {
-            targetField.val(this.value);
+            targetField.val(e.target.value);
           }
         }
-      });
+      }
+    }
+
+    for (var sourceId in settings.copyFieldValue) {
+      if (settings.copyFieldValue.hasOwnProperty(sourceId)) {
+        $('#' + sourceId).once('copy-field-values').bind('blur', blurCopyFieldValueHandler);
+      }
     }
   }
 };