diff --git a/nock/nock.d.ts b/nock/nock.d.ts
index db6d5df93..b6803ca89 100644
--- a/nock/nock.d.ts
+++ b/nock/nock.d.ts
@@ -58,7 +58,7 @@ declare module "nock" {
 			
 			matchHeader(name: string, value: string): Scope;
 			matchHeader(name: string, regex: RegExp): Scope;
-			matchHeader(name: string, fn: (value: string) => bool): Scope;
+			matchHeader(name: string, fn: (value: string) => boolean): Scope;
 
 			filteringPath(regex: RegExp, replace: string): Scope;
 			filteringPath(fn: (path: string) => string): Scope;