Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.1136
diff -u -r1.1136 user.module
--- modules/user/user.module	12 Mar 2010 15:56:30 -0000	1.1136
+++ modules/user/user.module	16 Mar 2010 06:38:14 -0000
@@ -2698,32 +2698,39 @@
 }
 
 /**
- * Grant permissions to a user role.
+ * Grants permissions to a user role.
  *
  * @param $rid
  *   The ID of a user role to alter.
  * @param $permissions
- *   A list of permission names to grant.
+ *   An array of permission names to grant. Non-existing permissions are
+ *   ignored.
  *
  * @see user_role_change_permissions()
  * @see user_role_revoke_permissions()
  */
 function user_role_grant_permissions($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();
-  }
 
-  // Clear the user access cache.
-  drupal_static_reset('user_access');
-  drupal_static_reset('user_role_permissions');
+  // Ignore non-existing permissions.
+  $permissions = array_intersect($permissions, array_keys($modules));
+
+  if ($permissions) {
+    // Grant new permissions for the role.
+    foreach ($permissions as $name) {
+      db_merge('role_permission')
+        ->key(array(
+          'rid' => $rid,
+          'permission' => $name,
+          'module' => $modules[$name],
+        ))
+        ->execute();
+    }
+
+    // Clear the user access cache.
+    drupal_static_reset('user_access');
+    drupal_static_reset('user_role_permissions');
+  }
 }
 
 /**