diff --git a/src/blutui.spec.ts b/src/blutui.spec.ts
index 7f3a903..98b6df3 100644
--- a/src/blutui.spec.ts
+++ b/src/blutui.spec.ts
@@ -47,6 +47,22 @@ describe('Blutui', () => {
       })
     })
 
+    describe('when access token and fetch function are provided to the constructor', () => {
+      it('initalizes', async () => {
+        // Example from JWT.io
+        const token =
+          'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c'
+        expect(
+          () =>
+            new Blutui(token, {
+              request: {
+                fetch: fetch,
+              },
+            })
+        ).not.toThrow()
+      })
+    })
+
     describe('version', () => {
       it('matches the version in `package.json`', async () => {
         const blutui = new Blutui('eyJhbGciOi')
diff --git a/src/blutui.ts b/src/blutui.ts
index ae6886b..ad17b06 100644
--- a/src/blutui.ts
+++ b/src/blutui.ts
@@ -53,12 +53,16 @@ export class Blutui {
 
     const useAgent: string = `blutui-node/${VERSION}`
 
-    this.client = new Client(this.baseURL, {
-      headers: {
-        Authorization: `Bearer ${this.accessToken}`,
-        'User-Agent': useAgent,
+    this.client = new Client(
+      this.baseURL,
+      {
+        headers: {
+          Authorization: `Bearer ${this.accessToken}`,
+          'User-Agent': useAgent,
+        },
       },
-    })
+      options.request?.fetch
+    )
   }
 
   /**
diff --git a/src/types.ts b/src/types.ts
index 76320ab..6e74e06 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -3,7 +3,8 @@
 export interface BlutuiOptions {
   apiHostname?: string
   request?: {
-    fetch?: typeof fetch
+    // biome-ignore lint/suspicious/noExplicitAny: We want developers to be able to use node-fetch
+    fetch?: any
   }
 }
 
diff --git a/src/utils/client.ts b/src/utils/client.ts
index f4b4da9..0411308 100644
--- a/src/utils/client.ts
+++ b/src/utils/client.ts
@@ -3,10 +3,24 @@ import { FetchException } from '../exceptions'
 const API_VERSION = 'v1'
 
 export class Client {
+  private readonly _fetchFn
+
+  /**
+   * Create a new client instance.
+   */
   constructor(
     readonly baseURL: string,
-    readonly options?: RequestInit
-  ) {}
+    readonly options?: RequestInit,
+    fetchFn?: typeof fetch
+  ) {
+    this._fetchFn = fetchFn || globalThis.fetch
+
+    if (!this._fetchFn) {
+      throw new Error(
+        'Fetch function not defined in the global scope and no replacement was provided.'
+      )
+    }
+  }
 
   async get(
     path: string,
@@ -80,7 +94,7 @@ export class Client {
   }
 
   private async fetch(url: string, options?: RequestInit) {
-    const response = await fetch(url, {
+    const response = await this._fetchFn(url, {
       ...this.options,
       ...options,
       headers: {