diff --git a/src/wcocr.ts b/src/wcocr.ts
index 662342d..a2207d1 100644
--- a/src/wcocr.ts
+++ b/src/wcocr.ts
@@ -65,7 +65,7 @@ export class WechatOCRClient {
   }
 
   public async recognize(image: Buffer): Promise<string> {
-    const tempPath = join(tmpdir(), `wechat-ocr-temp-${randomBytes(16).toString('hex')}.png`)
+    const tempPath = join(tmpdir(), `wechat-ocr-${randomBytes(16).toString('hex')}.tmp`)
     await writeFile(tempPath, image)
 
     try {