diff --git a/src/client.ts b/src/client.ts
index 1598ef34b..f9c54126b 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -2470,7 +2470,7 @@ export class MatrixClient extends EventEmitter {
      */
     // TODO: Verify types
     public async prepareKeyBackupVersion(
-        password: string,
+        password?: string,
         opts: IKeyBackupPrepareOpts = { secureSecretStorage: false },
     ): Promise<Pick<IPreparedKeyBackupVersion, "algorithm" | "auth_data" | "recovery_key">> {
         if (!this.crypto) {