From c90791d8cd7530262980501d7bea2eef12f533ec Mon Sep 17 00:00:00 2001
From: Abhishek Pai <contact@abhishekpai.co.uk>
Date: Sun, 29 Mar 2026 10:39:53 +0200
Subject: [PATCH 1/2] #1588: Allow negative linux epoch

---
 lib/CalDAV/Backend/PDO.php | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/lib/CalDAV/Backend/PDO.php b/lib/CalDAV/Backend/PDO.php
index 2767896434..a460ff506f 100644
--- a/lib/CalDAV/Backend/PDO.php
+++ b/lib/CalDAV/Backend/PDO.php
@@ -674,14 +674,6 @@ protected function getDenormalizedData($calendarData)
                     $lastOccurence = $end->getTimeStamp();
                 }
             }
-
-            // Ensure Occurence values are positive
-            if ($firstOccurence < 0) {
-                $firstOccurence = 0;
-            }
-            if ($lastOccurence < 0) {
-                $lastOccurence = 0;
-            }
         }
 
         // Destroy circular references to PHP will GC the object.

From 206f9cece9ef8a47dc14c5ccc52a84dfac9f6841 Mon Sep 17 00:00:00 2001
From: Abhishek Pai <abpai94@gmail.com>
Date: Fri, 3 Apr 2026 10:52:19 +0200
Subject: [PATCH 2/2] #1588: First and last occurence must be consecutive

---
 lib/CalDAV/Backend/PDO.php | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/CalDAV/Backend/PDO.php b/lib/CalDAV/Backend/PDO.php
index a460ff506f..fe445aeeb4 100644
--- a/lib/CalDAV/Backend/PDO.php
+++ b/lib/CalDAV/Backend/PDO.php
@@ -674,6 +674,12 @@ protected function getDenormalizedData($calendarData)
                     $lastOccurence = $end->getTimeStamp();
                 }
             }
+
+            // Ensure Occurence values are positive
+             if (date_diff($firstOccurence, $lastOccurence)->invert) {
+                 throw new \Sabre\DAV\Exception('Calendar firstOccurence and lastOccurence must be consecutive');
+             }
+
         }
 
         // Destroy circular references to PHP will GC the object.