diff --git a/inc/DAViCalSession.php b/inc/DAViCalSession.php
index 909e7860..1f7c8c13 100644
--- a/inc/DAViCalSession.php
+++ b/inc/DAViCalSession.php
@@ -121,7 +121,7 @@ class DAViCalSession extends Session
     /**
      * We allow basic auth to apply also, if present, though we check everything else first...
      */
-    if ( !$this->logged_in && $_SERVER['PHP_AUTH_USER'] != "" && $_SERVER['PHP_AUTH_PW'] != "" && ! $_COOKIE['NoAutoLogin'] ) {
+    if ( isset($_SERVER['PHP_AUTH_USER']) && !$this->logged_in && $_SERVER['PHP_AUTH_USER'] != "" && $_SERVER['PHP_AUTH_PW'] != "" && ! $_COOKIE['NoAutoLogin'] ) {
       if ( $this->Login($_SERVER['PHP_AUTH_USER'],$_SERVER['PHP_AUTH_PW'],true)) {
         setcookie('NoAutoLogin',1,0);
         return;