diff --git a/boost/spirit/home/qi/string/detail/tst.hpp b/boost/spirit/home/qi/string/detail/tst.hpp
index 4dbc3f9..51ff3f9 100644
--- a/boost/spirit/home/qi/string/detail/tst.hpp
+++ b/boost/spirit/home/qi/string/detail/tst.hpp
@@ -66,7 +66,7 @@ namespace boost { namespace spirit { namespace qi { namespace detail
         find(tst_node* start, Iterator& first, Iterator last, Filter filter)
         {
             if (first == last)
-                return false;
+                return NULL;
 
             Iterator i = first;
             Iterator latest = first;