diff --git a/src/request.ts b/src/request.ts
index 28408ba..b0428a4 100644
--- a/src/request.ts
+++ b/src/request.ts
@@ -74,8 +74,19 @@ const newRequestFromIncoming = (
   }
 
   if (!(method === 'GET' || method === 'HEAD')) {
-    // lazy-consume request body
-    init.body = Readable.toWeb(incoming) as ReadableStream<Uint8Array>
+    if ('rawBody' in incoming && incoming.rawBody instanceof Buffer) {
+      // In some environments (e.g. firebase functions), the body is already consumed.
+      // So we need to re-read the request body from `incoming.rawBody` if available.
+      init.body = new ReadableStream({
+        start(controller) {
+          controller.enqueue(incoming.rawBody)
+          controller.close()
+        },
+      })
+    } else {
+      // lazy-consume request body
+      init.body = Readable.toWeb(incoming) as ReadableStream<Uint8Array>
+    }
   }
 
   return new Request(url, init)
diff --git a/test/request.test.ts b/test/request.test.ts
index 999a371..0da2b6b 100644
--- a/test/request.test.ts
+++ b/test/request.test.ts
@@ -1,4 +1,5 @@
-import type { IncomingMessage } from 'node:http'
+import { IncomingMessage } from 'node:http'
+import { Socket } from 'node:net'
 import {
   newRequest,
   Request as LightweightRequest,
@@ -112,6 +113,29 @@ describe('Request', () => {
         } as IncomingMessage)
       }).toThrow(RequestError)
     })
+
+    it('Should be create request body from `req.rawBody` if it exists', async () => {
+      const rawBody = Buffer.from('foo')
+      const socket = new Socket()
+      const incomingMessage = new IncomingMessage(socket)
+      incomingMessage.method = 'POST'
+      incomingMessage.headers = {
+        host: 'localhost',
+      }
+      incomingMessage.url = '/foo.txt'
+      ;(incomingMessage as IncomingMessage & { rawBody: Buffer }).rawBody = rawBody
+      incomingMessage.push(rawBody)
+      incomingMessage.push(null)
+
+      for await (const chunk of incomingMessage) {
+        // consume body
+        expect(chunk).toBeDefined()
+      }
+
+      const req = newRequest(incomingMessage)
+      const text = await req.text()
+      expect(text).toBe('foo')
+    })
   })
 
   describe('GlobalRequest', () => {