--- a/boost/spirit/home/x3/string/detail/tst.hpp
+++ b/boost/spirit/home/x3/string/detail/tst.hpp
@@ -10,6 +10,7 @@
 #include <boost/call_traits.hpp>
 #include <boost/assert.hpp>
 
+#include <cstdint>
 #include <string>
 
 namespace boost { namespace spirit { namespace x3 { namespace detail
