diff --git a/backend/src/schemas.ts b/backend/src/schemas.ts
index 66f26637b842ed821022c98b7713efc431ad0dd3..aee0dcb1f14844859864a23795e5ca0683461dc7 100644
--- a/backend/src/schemas.ts
+++ b/backend/src/schemas.ts
@@ -13,16 +13,16 @@ export const Word = Type.Object({
 
 export const Game = Type.Object({
   id: Type.Readonly(Type.String({ format: "uuid" })),
-  began_at: Type.Optional(Type.String({ format: "date-time" })),
-  ended_at: Type.Optional(Type.String({ format: "date-time" })),
+  began_at: Nullable(Type.String({ format: "date-time" })),
+  ended_at: Nullable(Type.String({ format: "date-time" })),
 });
 
 export const Clue = Type.Object({
   id: Type.Readonly(Type.String({ format: "uuid" })),
   game_id: Type.Readonly(Type.String({ format: "uuid" })),
   word_id: Type.Readonly(Type.String({ format: "uuid" })),
-  began_at: Type.Optional(Type.String({ format: "date-time" })),
-  ended_at: Type.Optional(Type.String({ format: "date-time" })),
+  began_at: Nullable(Type.String({ format: "date-time" })),
+  ended_at: Nullable(Type.String({ format: "date-time" })),
 });
 
 export const Shot = Type.Object({