diff --git a/includes/cache.inc b/includes/cache.inc
index e21346a9e83022feff9ea56bad6bd7d73629bcd5..518ca313e2274ba4957ebc9e101bd6bd1f9496e8 100644
--- a/includes/cache.inc
+++ b/includes/cache.inc
@@ -102,7 +102,7 @@ function cache_get($cid, $table = 'cache') {
  */
 function cache_set($cid, $data, $table = 'cache', $expire = CACHE_PERMANENT, $headers = NULL) {
   $serialized = 0;
-  if (is_object($data) || is_array($data)) {
+  if (!is_string($data)) {
     $data = serialize($data);
     $serialized = 1;
   }