diff --git a/src/Microsoft.AspNetCore.SpaServices/npm/aspnet-prerendering/src/PrerenderingInterfaces.d.ts b/src/Microsoft.AspNetCore.SpaServices/npm/aspnet-prerendering/src/PrerenderingInterfaces.d.ts
index 446a242..248c4e8 100644
--- a/src/Microsoft.AspNetCore.SpaServices/npm/aspnet-prerendering/src/PrerenderingInterfaces.d.ts
+++ b/src/Microsoft.AspNetCore.SpaServices/npm/aspnet-prerendering/src/PrerenderingInterfaces.d.ts
@@ -8,7 +8,7 @@ interface RenderToStringCallback {
 
 interface RenderToStringResult {
     html: string;
-    statusCode: number;
+    statusCode?: number;
     globals?: { [key: string]: any };
 }