diff --git a/db/index.ts b/db/index.ts
index f346217..3704c05 100644
--- a/db/index.ts
+++ b/db/index.ts
@@ -64,7 +64,7 @@ export async function createBooking({
       'days',
       new mongoose.Error.ValidatorError({
         message: `${doubleBookedDays
-          .map(dateFormatFrontend)
+          .map((dateString) => dateFormatFrontend(new Date(dateString)))
           .join(', ')} schon gebucht`,
       })
     )