diff --git a/contracts/ETHMixer.sol b/contracts/ETHMixer.sol
index 803b179..70c14bf 100644
--- a/contracts/ETHMixer.sol
+++ b/contracts/ETHMixer.sol
@@ -24,6 +24,9 @@ contract ETHMixer is Mixer {
   }
 
   function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee, uint256 /* _refund */) internal {
+    require(msg.value == 0, "Message value is supposed to be zero for ETH mixer");
+    require(_refund == 0, "Message value is supposed to be zero for ETH mixer");
+
     _receiver.transfer(denomination - _fee);
     if (_fee > 0) {
       _relayer.transfer(_fee);