diff --git a/packages/backend/src/server/api/endpoints/users/following.ts b/packages/backend/src/server/api/endpoints/users/following.ts
index 6697e2d09d..fe642a9ddd 100644
--- a/packages/backend/src/server/api/endpoints/users/following.ts
+++ b/packages/backend/src/server/api/endpoints/users/following.ts
@@ -88,10 +88,21 @@ export const paramDef = {
 				sinceDate: { type: 'integer' },
 				untilDate: { type: 'integer' },
 				limit: { type: 'integer', minimum: 1, maximum: 100, default: 10 },
-				birthday: { ...birthdaySchema, nullable: true },
-				query: { type: 'string', nullable: true },
 			},
 		},
+		{
+			oneOf: [{
+				type: 'object',
+				properties: {
+					query: { type: 'string' },
+				},
+			}, {
+				type: 'object',
+				properties: {
+					birthday: { ...birthdaySchema, nullable: true },
+				},
+			}],
+		},
 	],
 } as const;
 
@@ -151,7 +162,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				.innerJoinAndSelect('following.followee', 'followee');
 
 			// query takes priority over birthday
-			if (ps.query) {
+			if ('query' in ps && ps.query != null) {
 				const searchQuery = ps.query;
 				const isUsername = searchQuery.startsWith('@') && !searchQuery.includes(' ') && searchQuery.indexOf('@', 1) === -1;
 
@@ -164,7 +175,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 						qb.orWhere('followee.usernameLower LIKE :username', { username: '%' + sqlLikeEscape(searchQuery.toLowerCase()) + '%' });
 					}
 				}));
-			} else if (ps.birthday) {
+			} else if ('birthday' in ps && ps.birthday != null) {
 				try {
 					const birthday = ps.birthday.substring(5, 10);
 					const birthdayUserQuery = this.userProfilesRepository.createQueryBuilder('user_profile');
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 254f1bcd73..90e723684f 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -34848,9 +34848,11 @@ export interface operations {
                     untilDate?: number;
                     /** @default 10 */
                     limit?: number;
+                } & ({
+                    query?: string;
+                } | {
                     birthday?: string | null;
-                    query?: string | null;
-                };
+                });
             };
         };
         responses: {