diff --git includes/menu.inc includes/menu.inc
index a3121c7..d5fc683 100644
--- includes/menu.inc
+++ includes/menu.inc
@@ -617,6 +617,22 @@ function _menu_check_access(&$item, $map) {
     }
     elseif (function_exists($callback)) {
       $item['access'] = call_user_func_array($callback, $arguments);
+      if (!isset($item['access'])) {
+        watchdog('menu.inc',
+          'Access callback function :callback failed to return a value when called with arguments :arguments',
+          array(':callback' => $callback, ':arguments' => var_export($arguments,1)),
+          WATCHDOG_WARNING,
+          'http://drupal.org/node/994992');
+        $item['access'] = FALSE;
+      }
+    }
+    else {
+      watchdog('menu.inc',
+        'Undefined access callback function :callback in router_item :item',
+        array(':callback' => $callback, ':item' => var_export($item,1)),
+        WATCHDOG_WARNING,
+        'http://drupal.org/node/994992');
+      $item['access'] = FALSE;
     }
   }
 }