diff --git a/inc/always.php.in b/inc/always.php.in
index 28c08bdd..74a0d631 100644
--- a/inc/always.php.in
+++ b/inc/always.php.in
@@ -45,7 +45,9 @@ function clean_get() {
 if(isset($_POST)) array_walk($_POST, 'filter_post');
 $_GET = clean_get();
 $_SERVER['REQUEST_URI'] = str_replace("&", "&", htmlspecialchars($_SERVER['REQUEST_URI']));
-$_SERVER['HTTP_REFERER'] = htmlspecialchars(@$_SERVER['HTTP_REFERER']);
+if (isset($_SERVER['HTTP_REFERER'])) {
+    $_SERVER['HTTP_REFERER'] = htmlspecialchars(@$_SERVER['HTTP_REFERER']);
+}
 
 
 
diff --git a/inc/caldav-PUT-functions.php b/inc/caldav-PUT-functions.php
index 1a2fb54c..e2afa3a9 100644
--- a/inc/caldav-PUT-functions.php
+++ b/inc/caldav-PUT-functions.php
@@ -1434,7 +1434,7 @@ function write_resource( DAVResource $resource, $caldav_data, DAVResource $colle
     $duration = $first->GetPValue('DURATION');
     $oldduration = $oldfirst->GetPValue('DURATION');
     $organizer = $vcal->GetOrganizer();
-    if (strcmp($duration, $oldduration)) $modified = true;
+    if (isset($duration) && isset($oldduration) && strcmp($duration, $oldduration)) $modified = true;
     if (($modified == true) && !($organizer === false || empty($organizer))) {
       dbg_error_log( 'PUT', "event time attributes have been modified, reset all attendees' PARTSTAT to NEEDS-ACTION.");
       $organizer_email = preg_replace( '/^mailto:/i', '', $organizer->Value() );