diff --git a/packages/backend/src/models/User.ts b/packages/backend/src/models/User.ts
index c282fa327f..b2b13e1724 100644
--- a/packages/backend/src/models/User.ts
+++ b/packages/backend/src/models/User.ts
@@ -430,6 +430,22 @@ export type MiPartialRemoteUser = Partial<MiUser> & {
 	uri: string;
 };
 
+export function isRemoteUser(user: MiUser): user is MiRemoteUser;
+export function isRemoteUser<U extends PartialUser>(user: U): user is PartialRemoteUser<U>;
+export function isRemoteUser(user: { host: string | null }): user is { host: string } {
+	return user.host != null;
+}
+
+export function isLocalUser(user: MiUser): user is MiLocalUser;
+export function isLocalUser<U extends PartialUser>(user: U): user is PartialLocalUser<U>;
+export function isLocalUser(user: { host: string | null }): user is { host: null } {
+	return user.host == null;
+}
+
+type PartialUser = Partial<MiUser> & { host: string | null, uri?: string | null };
+type PartialLocalUser<U extends PartialUser> = U & { host: null, uri?: null };
+type PartialRemoteUser<U extends PartialUser> = U & { host: string, uri?: string };
+
 export const localUsernameSchema = { type: 'string', pattern: /^\w{1,20}$/.toString().slice(1, -1) } as const;
 export const passwordSchema = { type: 'string', minLength: 1 } as const;
 export const nameSchema = { type: 'string', minLength: 1, maxLength: 50 } as const;