diff --git a/chai/chai.d.ts b/chai/chai.d.ts
index 059e835b84..6774a932fa 100644
--- a/chai/chai.d.ts
+++ b/chai/chai.d.ts
@@ -6,7 +6,7 @@
 
 declare module chai {
 
-    function expect(target: any): Expect;
+    function expect(target: any, message?: string): Expect;
 
     // Provides a way to extend the internals of Chai
     function use(fn: (chai: any, utils: any) => void);