diff --git a/index.js b/index.js
index bc4a1cc..e2f1ce0 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,6 @@
 const fetch = require('node-fetch');
 const fs = require('fs');
+const { URLSearchParams } = require('url');
 const crypto = require('crypto');
 const path = require('path');
 
@@ -9,6 +10,29 @@ function md5(str) {
   return crypto.createHash('md5').update(str).digest('hex');
 }
 
+function getBodyCacheKeyJson(body) {
+  if (typeof body === 'string') {
+    return body;
+  } if (body instanceof URLSearchParams) {
+    return body.toString();
+  }
+
+  return body;
+}
+
+function getCacheKey(requestArguments) {
+  const resource = requestArguments[0];
+  const init = requestArguments[1] || {};
+
+  const resourceCacheKeyJson = typeof resource === 'string' ? { url: resource } : { ...resource };
+  const initCacheKeyJson = { ...init };
+
+  resourceCacheKeyJson.body = getBodyCacheKeyJson(resourceCacheKeyJson.body);
+  initCacheKeyJson.body = getBodyCacheKeyJson(initCacheKeyJson.body);
+
+  return md5(JSON.stringify([resourceCacheKeyJson, initCacheKeyJson]));
+}
+
 async function createRawResponse(fetchRes) {
   const buffer = await fetchRes.buffer();
 
@@ -28,13 +52,8 @@ async function createRawResponse(fetchRes) {
 }
 
 async function getResponse(cacheDirPath, requestArguments) {
-  const [url, requestInit, ...rest] = requestArguments;
-  const requestParams = requestInit.body
-    ? ({ ...requestInit, body: typeof requestInit.body === 'object' ? requestInit.body.toString() : requestInit.body })
-    : requestInit;
-
-  const cacheHash = md5(JSON.stringify([url, requestParams, ...rest]));
-  const cachedFilePath = path.join(cacheDirPath, `${cacheHash}.json`);
+  const cacheKey = getCacheKey(requestArguments);
+  const cachedFilePath = path.join(cacheDirPath, `${cacheKey}.json`);
 
   try {
     const rawResponse = JSON.parse(await fs.promises.readFile(cachedFilePath));