diff --git a/memcache.inc b/memcache.inc
index da2f8be..1fa68b3 100644
--- a/memcache.inc
+++ b/memcache.inc
@@ -270,7 +270,7 @@ class MemCacheDrupal implements DrupalCacheInterface {
       // valid wildcard flushes in this bin.
       if (isset($this->wildcard_flushes[$this->bin][$wildcard_key])) {
         foreach ($this->wildcard_flushes[$this->bin][$wildcard_key] as $flush_length => $timestamp) {
-          if ($length >= $flush_length && $timestamp >= ($_SERVER['REQUEST_TIME'] - $this->invalidate)) {
+          if (is_int($flush_length) && $length >= $flush_length && $timestamp >= ($_SERVER['REQUEST_TIME'] - $this->invalidate)) {
             $wildcard = '.wildcard-' . substr($cid, 0, $flush_length);
             if (isset($wildcards[$this->bin][$wildcard])) {
               $matching[$wildcard] = $wildcards[$this->bin][$wildcard];