diff --git a/app/libs/wechat/weapp.rb b/app/libs/wechat/weapp.rb
index ca356b28d..cbf26efd2 100644
--- a/app/libs/wechat/weapp.rb
+++ b/app/libs/wechat/weapp.rb
@@ -22,8 +22,8 @@ class Wechat::Weapp
     end
 
     def decrypt(session_key, encrypted_data, iv)
-      session_key = Base64.decode64(session_key)
-      encrypted_data = Base64.decode64(encrypted_data)
+      session_key = Base64.decode64(session_key).force_encoding("utf-8")
+      encrypted_data = Base64.decode64(encrypted_data).force_encoding("utf-8")
       iv = Base64.decode64(iv)
 
       cipher = OpenSSL::Cipher::AES.new(128, :CBC)