diff --git a/src/dedupeRequestHash.ts b/src/dedupeRequestHash.ts
index 1e75bd7..81f6040 100644
--- a/src/dedupeRequestHash.ts
+++ b/src/dedupeRequestHash.ts
@@ -16,6 +16,30 @@ export type DedupeHashParams = {
   request?: Request
 }
 
+function toBase64(bytes: Uint8Array): string {
+  // Use Node Buffer when available, otherwise fall back to btoa for browser-like runtimes.
+  const maybeBuffer = (
+    globalThis as {
+      Buffer?: {
+        from(input: Uint8Array): { toString(encoding: string): string }
+      }
+    }
+  ).Buffer
+  if (maybeBuffer) {
+    return maybeBuffer.from(bytes).toString('base64')
+  }
+
+  let binary = ''
+  for (const byte of bytes) {
+    binary += String.fromCharCode(byte)
+  }
+  if (typeof btoa === 'function') {
+    return btoa(binary)
+  }
+
+  throw new Error('Base64 encoding is not available in this runtime')
+}
+
 export function dedupeRequestHash(
   params: DedupeHashParams
 ): string | undefined {
@@ -34,9 +58,9 @@ export function dedupeRequestHash(
   } else if (body instanceof URLSearchParams) {
     bodyString = body.toString()
   } else if (body instanceof ArrayBuffer) {
-    bodyString = Buffer.from(body).toString('base64')
+    bodyString = toBase64(new Uint8Array(body))
   } else if (body instanceof Uint8Array) {
-    bodyString = Buffer.from(body).toString('base64')
+    bodyString = toBase64(body)
   } else if (body instanceof Blob) {
     bodyString = `[blob:${body.type}:${body.size}]`
   } else if (body == null) {
diff --git a/test/plugins/dedupeRequestHash.test.ts b/test/plugins/dedupeRequestHash.test.ts
index 5eb1636..9f244d4 100644
--- a/test/plugins/dedupeRequestHash.test.ts
+++ b/test/plugins/dedupeRequestHash.test.ts
@@ -1,10 +1,18 @@
-import { describe, it, expect } from 'vitest'
+import { describe, it, expect, afterEach } from 'vitest'
 import {
   dedupeRequestHash,
   DedupeHashParams,
 } from '../../src/dedupeRequestHash'
 
 describe('dedupeRequestHash', () => {
+  const originalBuffer = (globalThis as { Buffer?: unknown }).Buffer
+  const originalBtoa = (globalThis as { btoa?: unknown }).btoa
+
+  afterEach(() => {
+    ;(globalThis as { Buffer?: unknown }).Buffer = originalBuffer
+    ;(globalThis as { btoa?: unknown }).btoa = originalBtoa
+  })
+
   it('returns undefined for FormData body', () => {
     const form = new FormData()
     form.append('foo', 'bar')
@@ -100,4 +108,36 @@ describe('dedupeRequestHash', () => {
     const hash = dedupeRequestHash(params)
     expect(hash).toContain('[unserializable-body]')
   })
+
+  it('falls back to btoa when Buffer is unavailable', () => {
+    ;(globalThis as { Buffer?: unknown }).Buffer = undefined
+    ;(globalThis as { btoa?: (input: string) => string }).btoa = (input) => {
+      if (input === 'abc') return 'YWJj'
+      throw new Error('unexpected btoa input')
+    }
+
+    const buf = new Uint8Array([97, 98, 99]).buffer
+    const params: DedupeHashParams = {
+      method: 'PUT',
+      url: 'https://example.com',
+      body: buf,
+    }
+
+    expect(dedupeRequestHash(params)).toBe('PUT|https://example.com|YWJj')
+  })
+
+  it('throws when neither Buffer nor btoa are available', () => {
+    ;(globalThis as { Buffer?: unknown }).Buffer = undefined
+    ;(globalThis as { btoa?: unknown }).btoa = undefined
+
+    const params: DedupeHashParams = {
+      method: 'PATCH',
+      url: 'https://example.com',
+      body: new Uint8Array([1, 2, 3]),
+    }
+
+    expect(() => dedupeRequestHash(params)).toThrow(
+      'Base64 encoding is not available in this runtime'
+    )
+  })
 })