diff --git a/cachefile.php b/cachefile.php
index a887294..dfe347e 100644
--- a/cachefile.php
+++ b/cachefile.php
@@ -157,7 +157,7 @@ class cachefile
       throw new \Exception ("CacheFile TTL invalid : not integer or negative".
       " : '$ttl'",
       500);
-    if (! is_string ($id) || ! is_integer ($id))
+    if (! is_string ($id) && ! is_integer ($id))
       throw new \Exception ("CacheFile write ID not a string : ".gettype ($id),
       500);