diff --git a/waffle-chai/src/types.ts b/waffle-chai/src/types.ts
index cac430065..d8597a614 100644
--- a/waffle-chai/src/types.ts
+++ b/waffle-chai/src/types.ts
@@ -33,6 +33,10 @@ declare namespace Chai {
     (value: any, message?: string): Assertion;
   }
 
+  interface CloseTo {
+    (expected: any, delta: number, message?: string): Assertion,
+  }
+
   interface AsyncAssertion extends Assertion, Promise<void> {
   }