diff --git a/package.json b/package.json
index a4c4d81..7265c1c 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,6 @@
 		"url": "sindresorhus.com"
 	},
 	"main": "dist/index.js",
-	"typings": "dist/index.d.ts",
 	"engines": {
 		"node": ">=4"
 	},
@@ -18,7 +17,7 @@
 		"prerelease": "npm run build",
 		"pretest": "npm run compile -- --sourceMap",
 		"test": "npm run lint && nyc ava dist/test",
-		"lint": "tslint --project .",
+		"lint": "tslint --format stylish --project .",
 		"build": "npm run clean && webpack",
 		"compile": "npm run clean && tsc",
 		"clean": "del dist"
@@ -47,7 +46,7 @@
 		"object"
 	],
 	"devDependencies": {
-		"@sindresorhus/is": "^0.4.0",
+		"@sindresorhus/is": "^0.5.0",
 		"@types/node": "^8.0.31",
 		"ava": "*",
 		"awesome-typescript-loader": "^3.2.3",
@@ -62,6 +61,7 @@
 		"vali-date": "^1.0.0",
 		"webpack": "^3.8.1"
 	},
+	"typings": "dist/index.d.ts",
 	"nyc": {
 		"exclude": [
 			"dist/test"
diff --git a/source/lib/argument-error.ts b/source/lib/argument-error.ts
index 5168735..4e893cb 100644
--- a/source/lib/argument-error.ts
+++ b/source/lib/argument-error.ts
@@ -1,5 +1,5 @@
 export class ArgumentError extends Error {
-	constructor(message, context) {
+	constructor(message: string, context: Function) {
 		super(message);
 		// TODO: Node does not preserve the error name in output when using the below, why?
 		Error.captureStackTrace(this, context);
diff --git a/source/lib/predicates/array.ts b/source/lib/predicates/array.ts
index 1daa516..1c1a354 100644
--- a/source/lib/predicates/array.ts
+++ b/source/lib/predicates/array.ts
@@ -129,7 +129,7 @@ export class ArrayPredicate extends Predicate<any[]> {
 	 * @param predicate The predicate that should be applied against every individual item.
 	 */
 	ofType<T>(predicate: Predicate<T>) {
-		let error;
+		let error: string;
 
 		return this.addValidator({
 			message: () => error,
diff --git a/source/lib/predicates/number.ts b/source/lib/predicates/number.ts
index 784779c..5ada34b 100644
--- a/source/lib/predicates/number.ts
+++ b/source/lib/predicates/number.ts
@@ -1,4 +1,4 @@
-import * as is from '@sindresorhus/is';
+import is from '@sindresorhus/is';
 import {Predicate, Context} from './predicate';
 
 export class NumberPredicate extends Predicate<number> {
diff --git a/source/lib/predicates/predicate.ts b/source/lib/predicates/predicate.ts
index 88cafe0..f520535 100644
--- a/source/lib/predicates/predicate.ts
+++ b/source/lib/predicates/predicate.ts
@@ -1,4 +1,4 @@
-import * as is from '@sindresorhus/is';
+import is from '@sindresorhus/is';
 import {not} from '../operators/not';
 
 export interface Validator<T> {