diff --git a/flag.module b/flag.module
index b8fbcb4..b544142 100644
--- a/flag.module
+++ b/flag.module
@@ -2057,7 +2057,9 @@ function flag_set_sid($uid = NULL, $create = TRUE) {
     $uid = $GLOBALS['user']->uid;
   }
 
-  if (!isset($sids[$uid])) {
+  // Sets the sid if none was set. If the caller specified to create an sid and
+  // we have an invalid one, create it instead of returning the invalid sid.
+  if (!isset($sids[$uid]) || ($sids[$uid] == -1 && $create)) {
     if (module_exists('session_api') && session_api_available() && $uid == 0) {
       $sids[$uid] = session_api_get_sid($create);
     }