diff --git a/app/features/calendar/routes/calendar.new.tsx b/app/features/calendar/routes/calendar.new.tsx
index 0b7403e37..124593b37 100644
--- a/app/features/calendar/routes/calendar.new.tsx
+++ b/app/features/calendar/routes/calendar.new.tsx
@@ -93,58 +93,75 @@ export const meta: MetaFunction = (args) => {
   return [{ title: data.title }];
 };
 
-const newCalendarEventActionSchema = z.object({
-  eventToEditId: z.preprocess(actualNumber, id.nullish()),
-  name: z
-    .string()
-    .min(CALENDAR_EVENT.NAME_MIN_LENGTH)
-    .max(CALENDAR_EVENT.NAME_MAX_LENGTH),
-  description: z.preprocess(
-    falsyToNull,
-    z.string().max(CALENDAR_EVENT.DESCRIPTION_MAX_LENGTH).nullable(),
-  ),
-  date: z.preprocess(
-    toArray,
-    z
-      .array(z.preprocess(date, z.date().min(MIN_DATE).max(MAX_DATE)))
-      .min(1)
-      .max(CALENDAR_EVENT.MAX_AMOUNT_OF_DATES),
-  ),
-  bracketUrl: z
-    .string()
-    .url()
-    .max(CALENDAR_EVENT.BRACKET_URL_MAX_LENGTH)
-    .default("https://sendou.ink"),
-  discordInviteCode: z.preprocess(
-    falsyToNull,
-    z.string().max(CALENDAR_EVENT.DISCORD_INVITE_CODE_MAX_LENGTH).nullable(),
-  ),
-  tags: z.preprocess(
-    processMany(safeJSONParse, removeDuplicates),
-    z
-      .array(
-        z
-          .string()
-          .refine((val) =>
-            CALENDAR_EVENT.TAGS.includes(val as CalendarEventTag),
-          ),
-      )
-      .nullable(),
-  ),
-  badges: z.preprocess(
-    processMany(safeJSONParse, removeDuplicates),
-    z.array(id).nullable(),
-  ),
-  pool: z.string().optional(),
-  toToolsEnabled: z.preprocess(checkboxValueToBoolean, z.boolean()),
-  toToolsMode: z.enum(["ALL", "SZ", "TC", "RM", "CB"]).optional(),
-});
+const newCalendarEventActionSchema = z
+  .object({
+    eventToEditId: z.preprocess(actualNumber, id.nullish()),
+    name: z
+      .string()
+      .min(CALENDAR_EVENT.NAME_MIN_LENGTH)
+      .max(CALENDAR_EVENT.NAME_MAX_LENGTH),
+    description: z.preprocess(
+      falsyToNull,
+      z.string().max(CALENDAR_EVENT.DESCRIPTION_MAX_LENGTH).nullable(),
+    ),
+    date: z.preprocess(
+      toArray,
+      z
+        .array(z.preprocess(date, z.date().min(MIN_DATE).max(MAX_DATE)))
+        .min(1)
+        .max(CALENDAR_EVENT.MAX_AMOUNT_OF_DATES),
+    ),
+    bracketUrl: z
+      .string()
+      .url()
+      .max(CALENDAR_EVENT.BRACKET_URL_MAX_LENGTH)
+      .default("https://sendou.ink"),
+    discordInviteCode: z.preprocess(
+      falsyToNull,
+      z.string().max(CALENDAR_EVENT.DISCORD_INVITE_CODE_MAX_LENGTH).nullable(),
+    ),
+    tags: z.preprocess(
+      processMany(safeJSONParse, removeDuplicates),
+      z
+        .array(
+          z
+            .string()
+            .refine((val) =>
+              CALENDAR_EVENT.TAGS.includes(val as CalendarEventTag),
+            ),
+        )
+        .nullable(),
+    ),
+    badges: z.preprocess(
+      processMany(safeJSONParse, removeDuplicates),
+      z.array(id).nullable(),
+    ),
+    pool: z.string().optional(),
+    toToolsEnabled: z.preprocess(checkboxValueToBoolean, z.boolean()),
+    toToolsMode: z.enum(["ALL", "SZ", "TC", "RM", "CB"]).optional(),
+  })
+  .refine(
+    async (schema) => {
+      if (schema.eventToEditId) {
+        const eventToEdit = await CalendarRepository.findById({
+          id: schema.eventToEditId,
+        });
+        return schema.date.length === 1 || !eventToEdit?.tournamentId;
+      } else {
+        return schema.date.length === 1 || !schema.toToolsEnabled;
+      }
+    },
+    {
+      message: "Tournament must have exactly one date",
+    },
+  );
 
 export const action: ActionFunction = async ({ request }) => {
   const user = await requireUser(request);
   const data = await parseRequestFormData({
     request,
     schema: newCalendarEventActionSchema,
+    parseAsync: true,
   });
 
   validate(canAddNewEvent(user), "Not authorized", 401);
diff --git a/app/features/tournament/TournamentRepository.server.ts b/app/features/tournament/TournamentRepository.server.ts
index f112293dc..7aab477d7 100644
--- a/app/features/tournament/TournamentRepository.server.ts
+++ b/app/features/tournament/TournamentRepository.server.ts
@@ -10,7 +10,6 @@ export async function findById(id: number) {
   const row = await db
     .selectFrom("Tournament")
     .innerJoin("CalendarEvent", "Tournament.id", "CalendarEvent.tournamentId")
-    // TODO: it does not support multiple dates
     .innerJoin(
       "CalendarEventDate",
       "CalendarEvent.id",
diff --git a/app/utils/remix.ts b/app/utils/remix.ts
index 6b2f2b52e..1ff71dd4e 100644
--- a/app/utils/remix.ts
+++ b/app/utils/remix.ts
@@ -47,12 +47,18 @@ export function parseSearchParams<T extends z.ZodTypeAny>({
 export async function parseRequestFormData<T extends z.ZodTypeAny>({
   request,
   schema,
+  parseAsync,
 }: {
   request: Request;
   schema: T;
+  parseAsync?: boolean;
 }): Promise<z.infer<T>> {
   try {
-    return schema.parse(formDataToObject(await request.formData()));
+    const parsed = parseAsync
+      ? await schema.parseAsync(formDataToObject(await request.formData()))
+      : schema.parse(formDataToObject(await request.formData()));
+
+    return parsed;
   } catch (e) {
     if (e instanceof z.ZodError) {
       console.error(e);