diff --git a/components/GuestsRoomsPicker/Form.tsx b/components/GuestsRoomsPicker/Form.tsx
index 4f0daed23..11d4dfb03 100644
--- a/components/GuestsRoomsPicker/Form.tsx
+++ b/components/GuestsRoomsPicker/Form.tsx
@@ -70,7 +70,11 @@ export default function GuestsRoomsPickerDialog({
     if (fieldState.invalid) trigger("rooms")
   }, [roomsValue, getFieldState, trigger])
 
-  const isInvalid = getFieldState("rooms").invalid
+  const isInvalid =
+    getFieldState("rooms").invalid ||
+    roomsValue.some((room) =>
+      room.childrenInRoom.some((child) => child.age === undefined)
+    )
   const canAddRooms = rooms.length < MAX_ROOMS
 
   return (