diff --git a/application/libraries/Caldav_sync.php b/application/libraries/Caldav_sync.php
index 3e6f71aa..a8e6ff67 100644
--- a/application/libraries/Caldav_sync.php
+++ b/application/libraries/Caldav_sync.php
@@ -70,7 +70,8 @@ class Caldav_sync
 
             $caldav_calendar = $provider['settings']['caldav_calendar'];
 
-            $caldav_event_id = $this->CI->ics_file->generate_uid($appointment['id']) . '.ics';
+            $caldav_event_id =
+                $appointment['id_caldav_calendar'] ?: $this->CI->ics_file->generate_uid($appointment['id']);
 
             $uri = $this->get_caldav_event_uri($caldav_calendar, $caldav_event_id);
 
@@ -107,7 +108,8 @@ class Caldav_sync
 
             $caldav_calendar = $provider['settings']['caldav_calendar'];
 
-            $caldav_event_id = $this->CI->ics_file->generate_uid($unavailability['id']) . '.ics';
+            $caldav_event_id =
+                $unavailability['id_caldav_calendar'] ?: $this->CI->ics_file->generate_uid($unavailability['id']);
 
             $uri = $this->get_caldav_event_uri($caldav_calendar, $caldav_event_id);
 
@@ -420,7 +422,7 @@ class Caldav_sync
      */
     private function get_caldav_event_uri(string $caldav_calendar, ?string $caldav_event_id = null): string
     {
-        return trim($caldav_calendar, '/') . ($caldav_event_id ? '/' . $caldav_event_id : '');
+        return trim($caldav_calendar, '/') . ($caldav_event_id ? '/' . $caldav_event_id . '.ics' : '');
     }
 
     /**
diff --git a/application/libraries/Ics_file.php b/application/libraries/Ics_file.php
index 64331982..4466936a 100644
--- a/application/libraries/Ics_file.php
+++ b/application/libraries/Ics_file.php
@@ -78,7 +78,7 @@ class Ics_file
             ->setEnd($appointment_end)
             ->setStatus('CONFIRMED')
             ->setSummary($service['name'])
-            ->setUid($this->generate_uid($appointment['id']));
+            ->setUid($appointment['id_caldav_calendar'] ?: $this->generate_uid($appointment['id']));
 
         if (!empty($service['location'])) {
             $location = new Location();
@@ -198,7 +198,7 @@ class Ics_file
             ->setEnd($unavailability_end)
             ->setStatus('CONFIRMED')
             ->setSummary('Unavailability')
-            ->setUid($this->generate_uid($unavailability['id']));
+            ->setUid($unavailability['id_caldav_calendar'] ?: $this->generate_uid($unavailability['id']));
 
         $event->setDescription(str_replace("\n", "\\n", (string) $unavailability['notes']));
 
diff --git a/application/libraries/Synchronization.php b/application/libraries/Synchronization.php
index f5fa8e47..aed977c5 100644
--- a/application/libraries/Synchronization.php
+++ b/application/libraries/Synchronization.php
@@ -36,6 +36,7 @@ class Synchronization
         $this->CI->load->model('appointments_model');
 
         $this->CI->load->library('google_sync');
+        $this->CI->load->library('caldav_sync');
     }
 
     /**