diff --git a/double_field.module b/double_field.module
index 8407e5f..39878e0 100644
--- a/double_field.module
+++ b/double_field.module
@@ -361,12 +361,14 @@ function double_field_i18n_strings_update($instance) {
     $i18n_keys[] = $widget_prefix . 'textfield-placeholder';
     $i18n_keys[] = $widget_prefix . 'textarea-placeholder';
     $i18n_keys[] = $widget_prefix . 'select-allowed_values';
-    foreach ($instance['display'] as $display_name => $display) {
-      $formatter_prefix = "display-$display_name-settings-";
-      $i18n_keys[] = $formatter_prefix . $subfield . '-prefix';
-      $i18n_keys[] = $formatter_prefix . $subfield . '-suffix';
-      $i18n_keys[] = $formatter_prefix . "table-$subfield-column_label";
-      $i18n_keys[] = $formatter_prefix . "table-number_column_label";
+    if (isset($instance['display'])) {
+      foreach ($instance['display'] as $display_name => $display) {
+        $formatter_prefix = "display-$display_name-settings-";
+        $i18n_keys[] = $formatter_prefix . $subfield . '-prefix';
+        $i18n_keys[] = $formatter_prefix . $subfield . '-suffix';
+        $i18n_keys[] = $formatter_prefix . "table-$subfield-column_label";
+        $i18n_keys[] = $formatter_prefix . "table-number_column_label";
+      }
     }
   }