diff --git a/advagg.module b/advagg.module
index b1763f7..b0d0547 100644
--- a/advagg.module
+++ b/advagg.module
@@ -2231,6 +2231,9 @@ function advagg_get_js($scope = 'header', array $javascript = array(), $ajax = F
     $javascript_static = &drupal_static('drupal_add_js', array());
     // Merge in any missing settings into the current data.
     foreach ($javascript_static['settings']['data'] as $key => $values) {
+      if (!isset($javascript['settings']['data'][$key])) {
+        continue;
+      }
       $diff = array_diff_key($values, $javascript['settings']['data'][$key]);
       if (!empty($diff)) {
         $javascript['settings']['data'][] = $values;