diff --git modules/user/user.module modules/user/user.module
index 505fe68..e9b578b 100644
--- modules/user/user.module
+++ modules/user/user.module
@@ -2785,13 +2785,10 @@ function user_role_grant_permissions($rid, array $permissions = array()) {
   $modules = user_permission_get_modules();
   // Grant new permissions for the role.
   foreach ($permissions as $name) {
-    db_merge('role_permission')
-      ->key(array(
-        'rid' => $rid,
-        'permission' => $name,
-        'module' => $modules[$name],
-      ))
-      ->execute();
+    if (empty($modules[$name])) {
+      throw new Exception(t('Unable to grant permission @permission.  The module in which it is defined is not enabled.', array('@permission' => $permission)));
+    }
+    user_role_grant_permission($rid, $name, $modules[$name]);
   }
 
   // Clear the user access cache.
@@ -2799,6 +2796,30 @@ function user_role_grant_permissions($rid, array $permissions = array()) {
   drupal_static_reset('user_role_permissions');
 }
 
+
+/**
+ * Grant a permission to a user role.
+ *
+ * @param $rid
+ *   The ID of a user role to alter.
+ * @param $permission
+ *   The name of the permission grant.
+ * @param $module
+ *   The name of the module the permission belongs to.
+ *
+ * @return int
+ *   Database query status code.
+ */
+function user_role_grant_permission($rid, $permission, $module) {
+  return db_merge('role_permission')
+    ->key(array(
+      'rid' => $rid,
+      'permission' => $permission,
+      'module' => $module,
+    ))
+    ->execute();
+}
+
 /**
  * Revoke permissions from a user role.
  *