diff --git a/modules/user/user.module b/modules/user/user.module
index fa580be..ce97d0f 100644
--- a/modules/user/user.module
+++ b/modules/user/user.module
@@ -2741,8 +2741,9 @@ function user_mail_tokens(&$replacements, $data, $options) {
 function user_roles($membersonly = FALSE, $permission = NULL) {
   $user_roles = &drupal_static(__FUNCTION__);
 
+  // Roles for specific permissions are not cached.
   if (empty($permission)) {
-    $cid = (int) $membersonly;
+    $cid = $membersonly ? DRUPAL_AUTHENTICATED_RID : DRUPAL_ANONYMOUS_RID;
     if (isset($user_roles[$cid])) {
       return $user_roles[$cid];
     }
@@ -2776,7 +2777,9 @@ function user_roles($membersonly = FALSE, $permission = NULL) {
     }
   }
 
-  if (isset($cid)) {
+  // Do not cache roles for specific permissions.  This data is not requested
+  // frequently enough to justify the additional memory use.
+  if (empty($permission)) {
     $user_roles[$cid] = $roles;
     return $user_roles[$cid];
   }