diff --git a/src/client.ts b/src/client.ts
index e08e3bee7c8..a294dcbd838 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -895,7 +895,7 @@ interface IRoomHierarchy {
 
 export interface TimestampToEventResponse {
     event_id: string;
-    origin_server_ts: string;
+    origin_server_ts: number;
 }
 
 interface IWhoamiResponse {