diff --git a/mocha/mocha.d.ts b/mocha/mocha.d.ts
index 717d080dc..8c1167def 100644
--- a/mocha/mocha.d.ts
+++ b/mocha/mocha.d.ts
@@ -4,8 +4,8 @@
 // DefinitelyTyped: https://github.com/borisyankov/DefinitelyTyped
 
 interface Mocha {
-    setup(options: MochaSetupOptions);
-    run(callback: () => void);
+    setup(options: MochaSetupOptions): void;
+    run(callback: () => void): void;
 }
 
 interface MochaSetupOptions {
@@ -18,7 +18,7 @@ declare var describe : {
     (description: string, spec: () => void): void;
     only(description: string, spec: () => void): void;
     skip(description: string, spec: () => void): void;
-    timeout(ms: number);
+    timeout(ms: number): void;
 }
 
 declare var it: {
@@ -28,22 +28,22 @@ declare var it: {
     only(expectation: string, assertion?: (done: (error?: Error) => void) => void): void;
     skip(expectation: string, assertion?: () => void): void;
     skip(expectation: string, assertion?: (done: (error?: Error) => void) => void): void;
-    timeout(ms: number);
+    timeout(ms: number): void;
 };
 
 declare function before(action: () => void): void;
 
-declare function before(action: (done: (failReason?) => void) => void): void;
+declare function before(action: (done: (error?: Error) => void) => void): void;
 
 declare function after(action: () => void): void;
 
-declare function after(action: (done: (failReason?) => void) => void): void;
+declare function after(action: (done: (error?: Error) => void) => void): void;
 
 declare function beforeEach(action: () => void): void;
 
-declare function beforeEach(action: (done: (failReason?) => void) => void): void;
+declare function beforeEach(action: (done: (error?: Error) => void) => void): void;
 
 declare function afterEach(action: () => void): void;
 
-declare function afterEach(action: (done: (failReason?) => void) => void): void;
+declare function afterEach(action: (done: (error?: Error) => void) => void): void;
 
diff --git a/sinon/sinon-tests.ts b/sinon/sinon-tests.ts
index 60751e908..b9b71c10e 100644
--- a/sinon/sinon-tests.ts
+++ b/sinon/sinon-tests.ts
@@ -1,7 +1,7 @@
 /// <reference path="sinon.d.ts" />
 
-function once(fn) {
-	var returnValue, called = false;
+function once(fn: Function) {
+	var returnValue: any, called = false;
 	return function () {
 		if (!called) {
 			called = true;
@@ -52,7 +52,7 @@ function testFive() {
 }
 
 var objectUnderTest: any = {
-	process: function (obj) {
+	process: function (obj: any) {
 		// It doesn't really matter what's here because the stub is going to replace this function
 		var dummy = true;
 		if (dummy) { return obj.success(99); } else { obj.failure(99); }
diff --git a/sinon/sinon.d.ts b/sinon/sinon.d.ts
index 61dfafa10..a33d65dfe 100644
--- a/sinon/sinon.d.ts
+++ b/sinon/sinon.d.ts
@@ -60,20 +60,20 @@ interface SinonSpy extends SinonSpyCallApi {
 	calledAfter(anotherSpy: SinonSpy): boolean;
 	calledWithNew(spy: SinonSpy): boolean;
 	withArgs(...args: any[]): SinonSpy;
-	alwaysCalledOn(obj: any);
-	alwaysCalledWith(...args: any[]);
-	alwaysCalledWithExactly(...args: any[]);
-	alwaysCalledWithMatch(...args: SinonMatcher[]);
-	neverCalledWith(...args: any[]);
-	neverCalledWithMatch(...args: SinonMatcher[]);
+	alwaysCalledOn(obj: any): boolean;
+	alwaysCalledWith(...args: any[]): boolean;
+	alwaysCalledWithExactly(...args: any[]): boolean;
+	alwaysCalledWithMatch(...args: SinonMatcher[]): boolean;
+	neverCalledWith(...args: any[]): boolean;
+	neverCalledWithMatch(...args: SinonMatcher[]): boolean;
 	alwaysThrew(): boolean;
-	alwaysThrew(type: string);
-	alwaysThrew(obj: any);
+	alwaysThrew(type: string): boolean;
+	alwaysThrew(obj: any): boolean;
 	alwaysReturned(): boolean;
 	invokeCallback(...args: any[]): void;
 	getCall(n: number): SinonSpyCall;
 	reset(): void;
-	printf(format: string, ...args: any[]);
+	printf(format: string, ...args: any[]): string;
 	restore(): void;
 }
 
@@ -208,7 +208,7 @@ interface SinonFakeXMLHttpRequest {
 	// Methods
 	restore(): void;
 	useFilters: boolean;
-	addFilter(filter: (method, url, async, username, password) => boolean): void;
+	addFilter(filter: (method: string, url: string, async: boolean, username: string, password: string) => boolean): void;
 	setResponseHeaders(headers: any): void;
 	setResponseBody(body: string): void;
 	respond(status: number, headers: any, body: string): void;