diff --git a/websocketpp/config/boost_config.hpp b/websocketpp/config/boost_config.hpp
index 0a0d2c9b6f..57671ccda4 100644
--- a/websocketpp/config/boost_config.hpp
+++ b/websocketpp/config/boost_config.hpp
@@ -41,7 +41,7 @@
     #define _WEBSOCKETPP_CPP11_FUNCTIONAL_
 #endif
 
-#ifndef BOOST_ASIO_HAS_STD_CHRONO
+#ifdef BOOST_ASIO_HAS_STD_CHRONO
     #define _WEBSOCKETPP_CPP11_CHRONO_
 #endif