diff --git a/plugins/libcalendaring/libcalendaring.php b/plugins/libcalendaring/libcalendaring.php
index 9b6b3fcc..e36940f6 100644
--- a/plugins/libcalendaring/libcalendaring.php
+++ b/plugins/libcalendaring/libcalendaring.php
@@ -1175,7 +1175,7 @@ class libcalendaring extends rcube_plugin
 
             foreach ($this->ical_parts as $mime_id) {
                 $part    = $this->ical_message->mime_parts[$mime_id];
-                $charset = $part->ctype_parameters['charset'] ?: RCUBE_CHARSET;
+                $charset = ($part->ctype_parameters['charset'] ?? '') ?: RCUBE_CHARSET;
                 $this->mail_ical_parser->import($this->ical_message->get_part_body($mime_id, true), $charset);
 
                 // check if the parsed object is an instance of a recurring event/task