diff --git a/concept_check_fail_expected.cpp b/concept_check_fail_expected.cpp
index b3a97b9..789bdf4 100644
--- a/concept_check_fail_expected.cpp
+++ b/concept_check_fail_expected.cpp
@@ -3,6 +3,10 @@
 // accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 
+#ifdef NDEBUG
+#  undef NDEBUG
+#endif
+
 #include <boost/concept_check.hpp>
 
 /*