From 896d76b218bcbd2c1a6da1d5e4f659503313c629 Mon Sep 17 00:00:00 2001
From: Ezra Freedman <38084742+ezra-freedman@users.noreply.github.com>
Date: Mon, 3 Nov 2025 07:55:20 -0500
Subject: [PATCH] Fix calendar all-day toggle date normalization (#27701)

---
 src/panels/calendar/dialog-calendar-event-editor.ts | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/panels/calendar/dialog-calendar-event-editor.ts b/src/panels/calendar/dialog-calendar-event-editor.ts
index 35a5ac91f7..e810f24685 100644
--- a/src/panels/calendar/dialog-calendar-event-editor.ts
+++ b/src/panels/calendar/dialog-calendar-event-editor.ts
@@ -332,6 +332,15 @@ class DialogCalendarEventEditor extends LitElement {
 
   private _allDayToggleChanged(ev) {
     this._allDay = ev.target.checked;
+    // When switching to all-day mode, normalize dates to midnight so time portions don't interfere with date comparisons
+    if (this._allDay && this._dtstart && this._dtend) {
+      this._dtstart = new Date(
+        formatDate(this._dtstart, this._timeZone!) + "T00:00:00"
+      );
+      this._dtend = new Date(
+        formatDate(this._dtend, this._timeZone!) + "T00:00:00"
+      );
+    }
   }
 
   private _startDateChanged(ev: CustomEvent) {