diff --git a/src/forms/CalendarForm/validation/validateExceptions.tsx b/src/forms/CalendarForm/validation/validateExceptions.tsx
index fc5c0cd2..ae121096 100644
--- a/src/forms/CalendarForm/validation/validateExceptions.tsx
+++ b/src/forms/CalendarForm/validation/validateExceptions.tsx
@@ -249,17 +249,12 @@ export function validateExceptionInterOverlaps(
     rows.map((row) => ({
       i: row.i,
       startDate: dayjs
-        .min(
-          row.rows
-          .map(({ startDate }) => dayjs(startDate))
-          .filter((date) => date.isValid())
-          )
+        .min(row.rows.map(({ startDate }) => dayjs(startDate))
+        .filter((date) => date !== null))
         .startOf('day'),
       endDate: dayjs
-        .max(
-          row.rows.map(({ endDate }) => dayjs(endDate))
-          .filter((date) => date.isValid())
-        )
+        .max(row.rows.map(({ endDate }) => dayjs(endDate))
+        .filter((date) => date !== null))
         .endOf('day')
     }));