diff --git a/inc/CalDAVRequest.php b/inc/CalDAVRequest.php
index 6670e1b8..ec9ad1f8 100644
--- a/inc/CalDAVRequest.php
+++ b/inc/CalDAVRequest.php
@@ -561,8 +561,10 @@ EOSQL;
         $params[':request_path'] = $this->path;
       }
       $qry = new AwlQuery( $sql, $params );
-      if ( $qry->Exec('caldav',__LINE__,__FILE__) && $permission_result = $qry->Fetch() )
-        $this->privileges |= bindec($permission_result->perm);
+      if ( $qry->Exec('caldav',__LINE__,__FILE__) && $permission_result = $qry->Fetch() ) {
+        $perm = $permission_result->perm;
+        if (isset($perm)) $this->privileges |= bindec($permission_result->perm);
+      }
 
       dbg_error_log( 'caldav', 'Restricted permissions for user accessing someone elses hierarchy: %s', decbin($this->privileges) );
       if ( isset($this->ticket) && $this->ticket->MatchesPath($this->path) ) {
diff --git a/inc/DAVResource.php b/inc/DAVResource.php
index 41e5209e..c4a919be 100644
--- a/inc/DAVResource.php
+++ b/inc/DAVResource.php
@@ -474,7 +474,7 @@ EOSQL;
           $this->collection->type = 'schedule-'. $matches[3]. 'box';
         else
           $this->collection->type = 'collection';
-        if ( strlen($row->external_url) > 8 ) {
+        if ( isset($row->external_url) && strlen($row->external_url) > 8 ) {
           $this->_is_external = true;
           if ( $row->external_type == 'calendar' )
             $this->collection->type = 'calendar';
diff --git a/inc/caldav-ACL.php b/inc/caldav-ACL.php
index 95f7f70c..54ae8dcc 100644
--- a/inc/caldav-ACL.php
+++ b/inc/caldav-ACL.php
@@ -174,7 +174,8 @@ function process_ace( $grantor, $by_principal, $by_collection, $ace ) {
 
     case 'DAV::authenticated':
       $principal_type = 'authenticated';
-      if ( bindec($grantor->GetProperty('default_privileges')) == $privileges ) break; // There is no change, so skip it
+      $grant_default_privs = $grantor->GetProperty('default_privileges');
+      if ( isset($grant_default_privs) && bindec($grant_default_privs) == $privileges ) break; // There is no change, so skip it
       $sqlparms = array( ':privileges' => $privileges );
       if ( isset($by_collection) ) {
         $sql = 'UPDATE collection SET default_privileges=:privileges::INT::BIT(24) WHERE collection_id=:by_collection';
diff --git a/inc/caldav-PUT-functions.php b/inc/caldav-PUT-functions.php
index e2afa3a9..4be240a3 100644
--- a/inc/caldav-PUT-functions.php
+++ b/inc/caldav-PUT-functions.php
@@ -210,7 +210,8 @@ function handle_schedule_request( $ical ) {
       dbg_error_log( "PUT", "not delivering to owner" );
       continue;
     }
-    if ( $attendee->GetParameterValue ( 'PARTSTAT' ) != 'NEEDS-ACTION' || preg_match ( '/^[35]\.[3-9]/',  $attendee->GetParameterValue ( 'SCHEDULE-STATUS' ) ) ) {
+    $schedule_status = $attendee->GetParameterValue ( 'SCHEDULE-STATUS' );
+    if ( $attendee->GetParameterValue ( 'PARTSTAT' ) != 'NEEDS-ACTION' || (isset($schedule_status) && preg_match ( '/^[35]\.[3-9]/',  $schedule_status ) ) ) {
       dbg_error_log( "PUT", "attendee %s does not need action", $attendee_email );
       continue;
     }
@@ -1430,7 +1431,7 @@ function write_resource( DAVResource $resource, $caldav_data, DAVResource $colle
     if (strcmp($dtstart, $olddtstart)) $modified = true;
     $dtend = $first->GetPValue('DTEND');
     $olddtend = $oldfirst->GetPValue('DTEND');
-    if (strcmp($dtend, $olddtend)) $modified = true;
+    if (isset($dtend) && isset($olddtend) && strcmp($dtend, $olddtend)) $modified = true;
     $duration = $first->GetPValue('DURATION');
     $oldduration = $oldfirst->GetPValue('DURATION');
     $organizer = $vcal->GetOrganizer();
@@ -1468,7 +1469,7 @@ function write_resource( DAVResource $resource, $caldav_data, DAVResource $colle
   $calitem_params[':due'] = $due;
   $dtstart = $first->GetPValue('DTSTART');
   if ( empty($dtstart) ) $dtstart = $due;
-  if (preg_match("/^1[0-8][0-9][0-9][01][0-9][0-3][0-9]$/", $dtstart))
+  if (isset($dtstart) && preg_match("/^1[0-8][0-9][0-9][01][0-9][0-3][0-9]$/", $dtstart))
      $dtstart = $dtstart . "T000000Z";
   $calitem_params[':dtstart'] = $dtstart;
 
diff --git a/inc/caldav-REPORT-calquery.php b/inc/caldav-REPORT-calquery.php
index 4c4d9874..0c4228c1 100644
--- a/inc/caldav-REPORT-calquery.php
+++ b/inc/caldav-REPORT-calquery.php
@@ -171,6 +171,9 @@ OR (first_instance_start IS NOT NULL AND ($new_cond))
         $search = $v->GetContent();
         $negate = $v->GetAttribute("negate-condition");
         $collation = $v->GetAttribute("collation");
+        if (! isset($collation)) {
+            $collation = '';
+        }
         switch( strtolower($collation) ) {
           case 'i;octet':
             $comparison = 'LIKE';