diff --git a/include/boost/preprocessor/slot.hpp b/include/boost/preprocessor/slot.hpp
index 1cad6e6..e0ef01f 100644
--- a/include/boost/preprocessor/slot.hpp
+++ b/include/boost/preprocessor/slot.hpp
@@ -12,6 +12,7 @@
 #  ************************************************************************** */
 #
 # include <boost/preprocessor/detail/cat.hpp>
+# include <boost/preprocessor/detail/line.hpp>
 #
 # define BOOST_PP_SLOT_LIMIT 5
 #