diff --git a/include/boost/function/detail/prologue.hpp b/include/boost/function/detail/prologue.hpp
index 1ef5f6e..ab2b323 100644
--- a/include/boost/function/detail/prologue.hpp
+++ b/include/boost/function/detail/prologue.hpp
@@ -11,6 +11,7 @@
 #define BOOST_FUNCTION_PROLOGUE_HPP
 #  include <cassert>
 #  include <algorithm>
+#  include <functional> // unary_function, binary_function
 #  include <boost/throw_exception.hpp>
 #  include <boost/config.hpp>
 #  include <boost/function/function_base.hpp>