diff --git a/src/matrix.ts b/src/matrix.ts
index 7a60404d2..e3f22c4c0 100644
--- a/src/matrix.ts
+++ b/src/matrix.ts
@@ -113,9 +113,9 @@ export function setCryptoStoreFactory(fac) {
     cryptoStoreFactory = fac;
 }
 
-
 interface ICreateClientOpts {
     baseUrl: string;
+    idBaseUrl?: string;
     store?: Store;
     cryptoStore?: CryptoStore;
     scheduler?: MatrixScheduler;