diff --git a/gulp-mocha/gulp-mocha.d.ts b/gulp-mocha/gulp-mocha.d.ts
index e6bc099c3..8d21b1323 100644
--- a/gulp-mocha/gulp-mocha.d.ts
+++ b/gulp-mocha/gulp-mocha.d.ts
@@ -7,6 +7,6 @@
 /// <reference path="../node/node.d.ts"/>
 
 declare module "gulp-mocha" {
-    function mocha(setupOptions: MochaSetupOptions): NodeJS.ReadWriteStream;
+    function mocha(setupOptions?: MochaSetupOptions): NodeJS.ReadWriteStream;
     export = mocha;
 }
\ No newline at end of file
diff --git a/gulp-replace/gulp-replace.d.ts b/gulp-replace/gulp-replace.d.ts
index 6607da98c..cf6ef7164 100644
--- a/gulp-replace/gulp-replace.d.ts
+++ b/gulp-replace/gulp-replace.d.ts
@@ -10,8 +10,12 @@ declare module "gulp-replace" {
         skipBinary?: boolean;
     }
 
-    function replace(pattern: string, replacement: string, opts?: Options): NodeJS.ReadWriteStream;
-    function replace(pattern: RegExp, replacement: string, opts?: Options): NodeJS.ReadWriteStream;
+    interface Replacer {
+      (match: string): string
+    }
+
+    function replace(pattern: string, replacement: string | Replacer, opts?: Options): NodeJS.ReadWriteStream;
+    function replace(pattern: RegExp, replacement: string | Replacer, opts?: Options): NodeJS.ReadWriteStream;
 
     export = replace;
 }
\ No newline at end of file