diff --git a/source/index.ts b/source/index.ts
index f819d82..ba578a4 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -2,7 +2,9 @@
 /// <reference lib="dom"/>
 /// <reference types="node"/>
 
-export type Class<T = unknown> = new (...args: any[]) => T;
+import {Class, TypedArray, ObservableLike, Primitive} from './types';
+
+export {Class, TypedArray, ObservableLike, Primitive};
 
 const typedArrayTypeNames = [
 	'Int8Array',
@@ -18,19 +20,6 @@ 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 +69,6 @@ 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 +299,6 @@ 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;
diff --git a/source/types.ts b/source/types.ts
new file mode 100644
index 0000000..8bdd0f5
--- /dev/null
+++ b/source/types.ts
@@ -0,0 +1,49 @@
+// Extracted from https://github.com/sindresorhus/type-fest/blob/78019f42ea888b0cdceb41a4a78163868de57555/index.d.ts
+
+/**
+Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).
+*/
+export type Primitive =
+	| null
+	| undefined
+	| string
+	| number
+	| boolean
+	| symbol
+	| bigint;
+
+// TODO: Remove the `= unknown` sometime  in the future when most users are on TS 3.5 as it's now the default
+/**
+Matches a [`class` constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
+*/
+export type Class<T = unknown, Arguments extends any[] = any[]> = new (...arguments_: Arguments) => T;
+
+/**
+Matches any [typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), like `Uint8Array` or `Float64Array`.
+*/
+export type TypedArray =
+	| Int8Array
+	| Uint8Array
+	| Uint8ClampedArray
+	| Int16Array
+	| Uint16Array
+	| Int32Array
+	| Uint32Array
+	| Float32Array
+	| Float64Array
+	| BigInt64Array
+	| BigUint64Array;
+
+declare global {
+	interface SymbolConstructor {
+		readonly observable: symbol;
+	}
+}
+
+/**
+Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
+*/
+export interface ObservableLike {
+	subscribe(observer: (value: unknown) => void): void;
+	[Symbol.observable](): ObservableLike;
+}