diff --git a/app/libs/wechat/weapp.rb b/app/libs/wechat/weapp.rb
index aed14128b..0a1cc5eed 100644
--- a/app/libs/wechat/weapp.rb
+++ b/app/libs/wechat/weapp.rb
@@ -24,7 +24,7 @@ class Wechat::Weapp
     def decrypt(session_key, encrypted_data, iv)
       session_key = Base64.decode64(session_key)
       encrypted_data = Base64.decode64(encrypted_data)
-      cd = CharDet.detect(content)
+      cd = CharDet.detect(encrypted_data)
       encrypted_data =
         if cd["encoding"] == 'GB18030' && cd['confidence'] > 0.8
           encrypted_data.encode('UTF-8', 'GBK', {:invalid => :replace, :undef => :replace, :replace => ' '})