diff --git a/modules/authcache_boost/authcache_boost.module b/modules/authcache_boost/authcache_boost.module
index ab85c54..01293bb 100644
--- a/modules/authcache_boost/authcache_boost.module
+++ b/modules/authcache_boost/authcache_boost.module
@@ -52,7 +52,8 @@ function authcache_boost_init() {
   global $conf, $_boost;
 
   // Force boost_normal_dir.
-  $conf['boost_normal_dir'] = authcache_is_default_key() ? BOOST_NORMAL_DIR : authcache_key();
+  $authcache_key = authcache_key();
+  $conf['boost_normal_dir'] = authcache_is_default_key($authcache_key) ? BOOST_NORMAL_DIR : $authcache_key;
 
   // Enforce addition of a vary-cookie directive into the .htaccess file within
   // the boost cache directory.