diff --git a/core/includes/batch.inc b/core/includes/batch.inc
index 27fb632..1594082 100644
--- a/core/includes/batch.inc
+++ b/core/includes/batch.inc
@@ -357,10 +357,10 @@ function _batch_next_set() {
   if (isset($batch['sets'][$batch['current_set'] + 1])) {
     $batch['current_set']++;
     $current_set = &_batch_current_set();
-    if (isset($current_set['form_submit']) && ($function = $current_set['form_submit']) && function_exists($function)) {
+    if (isset($current_set['form_submit']) && ($callable = $current_set['form_submit']) && is_callable($callable)) {
       // We use our stored copies of $form and $form_state to account for
       // possible alterations by previous form submit handlers.
-      $function($batch['form_state']['complete_form'], $batch['form_state']);
+      $callable($batch['form_state']['complete_form'], $batch['form_state']);
     }
     return TRUE;
   }
@@ -382,7 +382,7 @@ function _batch_finished() {
       if (isset($batch_set['file']) && is_file($batch_set['file'])) {
         include_once DRUPAL_ROOT . '/' . $batch_set['file'];
       }
-      if (function_exists($batch_set['finished'])) {
+      if (is_callable($batch_set['finished'])) {
         $queue = _batch_queue($batch_set);
         $operations = $queue->getAllItems();
         $batch_set['finished']($batch_set['success'], $batch_set['results'], $operations, format_interval($batch_set['elapsed'] / 1000));
@@ -438,11 +438,11 @@ function _batch_finished() {
     if (!empty($_batch['form_state']['rebuild'])) {
       $_SESSION['batch_form_state'] = $_batch['form_state'];
     }
-    $function = $_batch['redirect_callback'];
-    if (function_exists($function)) {
-      $function($_batch['source_url'], array('query' => array('op' => 'finish', 'id' => $_batch['id'])));
+    $callable = $_batch['redirect_callback'];
+    if (is_callable($callable)) {
+      $callable($_batch['source_url'], array('query' => array('op' => 'finish', 'id' => $_batch['id'])));
     }
-    elseif ($function === NULL) {
+    elseif ($callable === NULL) {
       // Default to RedirectResponse objects when nothing specified.
       $url = url($_batch['source_url'], array(
         'absolute' => TRUE,