--- a/boost/context/continuation.hpp
+++ b/boost/context/continuation.hpp
@@ -4,6 +4,9 @@
 //    (See accompanying file LICENSE_1_0.txt or copy at
 //          http://www.boost.org/LICENSE_1_0.txt)
 
+// BOOST_USE_UCONTEXT may be set in the installation's user config
+#include <boost/config.hpp>
+
 #if defined(BOOST_USE_UCONTEXT)
 #include <boost/context/continuation_ucontext.hpp>
 #elif defined(BOOST_USE_WINFIB)
--- a/boost/context/fiber.hpp
+++ b/boost/context/fiber.hpp
@@ -4,6 +4,9 @@
 //    (See accompanying file LICENSE_1_0.txt or copy at
 //          http://www.boost.org/LICENSE_1_0.txt)
 
+// BOOST_USE_UCONTEXT may be set in the installation's user config
+#include <boost/config.hpp>
+
 #if defined(BOOST_USE_UCONTEXT)
 #include <boost/context/fiber_ucontext.hpp>
 #elif defined(BOOST_USE_WINFIB)