diff --git a/include/boost/preprocessor/control/expr_if.hpp b/include/boost/preprocessor/control/expr_if.hpp
index 5e17b5b..76120fa 100644
--- a/include/boost/preprocessor/control/expr_if.hpp
+++ b/include/boost/preprocessor/control/expr_if.hpp
@@ -16,6 +16,7 @@
 # define BOOST_PREPROCESSOR_CONTROL_EXPR_IF_HPP
 #
 # include <boost/preprocessor/config/config.hpp>
+# include <boost/preprocessor/control/expr_iif.hpp>
 #
 # /* BOOST_PP_EXPR_IF */
 #