diff --git a/src/client.ts b/src/client.ts
index f590ddf0d..0dcff1d75 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -1009,7 +1009,7 @@ export class MatrixClient extends EventEmitter {
      * state change events.
      * @param {Object=} opts Options to apply when syncing.
      */
-    public async startClient(opts: IStartClientOpts): Promise<void> {
+    public async startClient(opts?: IStartClientOpts): Promise<void> {
         if (this.clientRunning) {
             // client is already running.
             return;