diff --git a/package.json b/package.json
index 9e7b3d3..718909d 100644
--- a/package.json
+++ b/package.json
@@ -46,6 +46,9 @@
 		"typeguards",
 		"types"
 	],
+	"dependencies": {
+		"type-fest": "^0.16.0"
+	},
 	"devDependencies": {
 		"@sindresorhus/tsconfig": "^0.7.0",
 		"@types/jsdom": "^16.1.0",
diff --git a/source/index.ts b/source/index.ts
index f819d82..86ba271 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -2,7 +2,7 @@
 /// <reference lib="dom"/>
 /// <reference types="node"/>
 
-export type Class<T = unknown> = new (...args: any[]) => T;
+import {Class, TypedArray, ObservableLike, Primitive} from 'type-fest';
 
 const typedArrayTypeNames = [
 	'Int8Array',
@@ -18,19 +18,6 @@ const typedArrayTypeNames = [
 	'BigUint64Array'
 ] as const;
 
-export type TypedArray =
-	| Int8Array
-	| Uint8Array
-	| Uint8ClampedArray
-	| Int16Array
-	| Uint16Array
-	| Int32Array
-	| Uint32Array
-	| Float32Array
-	| Float64Array
-	| BigInt64Array
-	| BigUint64Array;
-
 type TypedArrayTypeName = typeof typedArrayTypeNames[number];
 
 function isTypedArrayName(name: unknown): name is TypedArrayTypeName {
@@ -80,15 +67,6 @@ const primitiveTypeNames = [
 	'symbol'
 ] as const;
 
-export type Primitive =
-	| null
-	| undefined
-	| string
-	| number
-	| bigint
-	| boolean
-	| symbol;
-
 type PrimitiveTypeName = typeof primitiveTypeNames[number];
 
 function isPrimitiveTypeName(name: unknown): name is PrimitiveTypeName {
@@ -319,11 +297,6 @@ is.domElement = (value: unknown): value is HTMLElement => {
 	DOM_PROPERTIES_TO_CHECK.every(property => property in value);
 };
 
-export interface ObservableLike {
-	subscribe(observer: (value: unknown) => void): void;
-	[Symbol.observable](): ObservableLike;
-}
-
 is.observable = (value: unknown): value is ObservableLike => {
 	if (!value) {
 		return false;