diff --git a/signalr/signalr.d.ts b/signalr/signalr.d.ts
index 9b0131f6cb..6fe6b87896 100644
--- a/signalr/signalr.d.ts
+++ b/signalr/signalr.d.ts
@@ -180,6 +180,7 @@ declare namespace SignalR {
     interface ConnectionError extends Error {
         context: ConnectionErrorContext;
         transport?: string;
+        source?: string;
     }
 
     interface Connection {