diff --git a/packages/backend/src/server/api/endpoints/notes/drafts/create.ts b/packages/backend/src/server/api/endpoints/notes/drafts/create.ts
index 880f4964a1..efb5ee01d1 100644
--- a/packages/backend/src/server/api/endpoints/notes/drafts/create.ts
+++ b/packages/backend/src/server/api/endpoints/notes/drafts/create.ts
@@ -135,6 +135,18 @@ export const meta = {
 			code: 'CANNOT_RENOTE_TO_EXTERNAL',
 			id: 'ed1952ac-2d26-4957-8b30-2deda76bedf7',
 		},
+
+		scheduledAtRequired: {
+			message: 'scheduledAt is required when isActuallyScheduled is true.',
+			code: 'SCHEDULED_AT_REQUIRED',
+			id: '15e28a55-e74c-4d65-89b7-8880cdaaa87d',
+		},
+
+		scheduledAtMustBeInFuture: {
+			message: 'scheduledAt must be in the future.',
+			code: 'SCHEDULED_AT_MUST_BE_IN_FUTURE',
+			id: 'e4bed6c9-017e-4934-aed0-01c22cc60ec1',
+		},
 	},
 
 	limit: {
@@ -252,6 +264,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 							throw new ApiError(meta.errors.cannotReplyToSpecifiedVisibilityNoteWithExtendedVisibility);
 						case 'c3275f19-4558-4c59-83e1-4f684b5fab66':
 							throw new ApiError(meta.errors.tooManyScheduledNotes);
+						case '94a89a43-3591-400a-9c17-dd166e71fdfa':
+							throw new ApiError(meta.errors.scheduledAtRequired);
+						case 'b34d0c1b-996f-4e34-a428-c636d98df457':
+							throw new ApiError(meta.errors.scheduledAtMustBeInFuture);
 						default:
 							throw err;
 					}
diff --git a/packages/backend/src/server/api/endpoints/notes/drafts/update.ts b/packages/backend/src/server/api/endpoints/notes/drafts/update.ts
index 9a2e2ca415..2900e0cb0d 100644
--- a/packages/backend/src/server/api/endpoints/notes/drafts/update.ts
+++ b/packages/backend/src/server/api/endpoints/notes/drafts/update.ts
@@ -165,6 +165,18 @@ export const meta = {
 			code: 'TOO_MANY_SCHEDULED_NOTES',
 			id: '02f5df79-08ae-4a33-8524-f1503c8f6212',
 		},
+
+		scheduledAtRequired: {
+			message: 'scheduledAt is required when isActuallyScheduled is true.',
+			code: 'SCHEDULED_AT_REQUIRED',
+			id: 'fe9737d5-cc41-498c-af9d-149207307530',
+		},
+
+		scheduledAtMustBeInFuture: {
+			message: 'scheduledAt must be in the future.',
+			code: 'SCHEDULED_AT_MUST_BE_IN_FUTURE',
+			id: 'ed1a6673-d0d1-4364-aaae-9bf3f139cbc5',
+		},
 	},
 
 	limit: {
@@ -295,6 +307,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 							throw new ApiError(meta.errors.containsTooManyMentions);
 						case 'bacdf856-5c51-4159-b88a-804fa5103be5':
 							throw new ApiError(meta.errors.tooManyScheduledNotes);
+						case '94a89a43-3591-400a-9c17-dd166e71fdfa':
+							throw new ApiError(meta.errors.scheduledAtRequired);
+						case 'b34d0c1b-996f-4e34-a428-c636d98df457':
+							throw new ApiError(meta.errors.scheduledAtMustBeInFuture);
 						default:
 							throw err;
 					}