Index: dmemcache.inc
===================================================================
--- dmemcache.inc       (revision 2436)
+++ dmemcache.inc       (working copy)
@@ -71,7 +71,8 @@
       // can be adjusted by setting the memcache_stampede_semaphore variable.
       // TODO: Can we log when a sempahore expires versus being intentionally
       // freed to track when this is happening?
-      if ($result->expire && $result->expire <= time() && $mc->add($full_key .'_semaphore', '', FALSE, variable_get('memcache_stampede_semaphore', 15))) {
+      if (isset($result->expire) && $result->expire !== CACHE_PERMANENT && $result->expire <= time() && $mc->add($full_key .'_semaphore', '', FALSE, variable_get('memcache_stampede_semaphore', 15))) {
+
         $result = FALSE;
       }
       else {