diff --git a/src/utils.ts b/src/utils.ts
index ee6216d..278ca2b 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1,7 +1,9 @@
 import { getCanonicalLocale } from '@nextcloud/l10n'
 
 export function toDateString(d: Date): string {
-	return d.toISOString().slice(0, 10)
+	const month = String(d.getMonth() + 1).padStart(2, '0')
+	const day = String(d.getDate()).padStart(2, '0')
+	return `${d.getFullYear()}-${month}-${day}`
 }
 
 const dateFormatter = new Intl.DateTimeFormat(getCanonicalLocale(), { dateStyle: 'long' })