diff --git a/cachefile.php b/cachefile.php
index e4a00ef..a887294 100644
--- a/cachefile.php
+++ b/cachefile.php
@@ -157,6 +157,9 @@ class cachefile
       throw new \Exception ("CacheFile TTL invalid : not integer or negative".
       " : '$ttl'",
       500);
+    if (! is_string ($id) || ! is_integer ($id))
+      throw new \Exception ("CacheFile write ID not a string : ".gettype ($id),
+      500);
 
     $this->garbage ();
     $fileCache = $this->directory."/".sha1 ($id);
@@ -192,6 +195,9 @@ class cachefile
     }
 
     $this->garbage ();
+    if (! is_string ($id) || ! is_integer ($id))
+      throw new \Exception ("CacheFile read ID not a string : ".gettype ($id),
+      500);
     $fileCache = $this->directory."/".sha1 ($id);
     if (!file_exists ($fileCache))
       return false;