diff -up ./lib/Event.php.fix ./lib/Event.php
--- ./lib/Event.php.fix	2017-10-13 14:30:50.754164418 +0200
+++ ./lib/Event.php	2017-10-13 14:31:04.412234396 +0200
@@ -795,7 +795,7 @@ abstract class Kronolith_Event
 
             // Tags
             if ($this->tags) {
-                if (count($this->tags == 1)) {
+                if (count($this->tags) == 1) {
                     $vEvent->setAttribute('CATEGORIES', $this->tags[0]);
                 } else {
                     $vEvent->setAttribute('CATEGORIES', '', array(), true, $this->tags);