diff --git a/contracts/MiniMeToken.sol b/contracts/MiniMeToken.sol
index 14be148d..d30237f1 100644
--- a/contracts/MiniMeToken.sol
+++ b/contracts/MiniMeToken.sol
@@ -482,6 +482,7 @@ contract MiniMeToken is Controlled {
     ///  set to 0, then the `proxyPayment` method is called which relays the
     ///  ether and creates tokens as described in the token controller contract
     function () public payable {
+        require(msg.data.length == 0);
         require(isContract(controller));
         require(TokenController(controller).proxyPayment.value(msg.value)(msg.sender));
     }