diff --git a/lib/composer/composer/ClassLoader.php b/lib/composer/composer/ClassLoader.php
index 95f7e0978ba..fce8549f078 100644
--- a/lib/composer/composer/ClassLoader.php
+++ b/lib/composer/composer/ClassLoader.php
@@ -279,7 +279,7 @@ class ClassLoader
      */
     public function setApcuPrefix($apcuPrefix)
     {
-        $this->apcuPrefix = function_exists('apcu_fetch') && ini_get('apc.enabled') ? $apcuPrefix : null;
+        $this->apcuPrefix = function_exists('apcu_fetch') && filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) ? $apcuPrefix : null;
     }
 
     /**