diff --git a/src/net/common/serverlobbythread.cpp b/src/net/common/serverlobbythread.cpp
index d76bc66e..ee5e8f02 100644
--- a/src/net/common/serverlobbythread.cpp
+++ b/src/net/common/serverlobbythread.cpp
@@ -1427,7 +1427,7 @@ ServerLobbyThread::AuthChallenge(boost::shared_ptr<SessionData> session, const s
 		OCTET_STRING_fromBuf(
 			&challenge->serverChallenge,
 			(char *)outChallenge.c_str(),
-			outChallenge.size());
+			(int)outChallenge.size());
 		GetSender().Send(session, packet);
 	}
 }