diff --git a/roottest/root/meta/genreflex/ROOT-5768/PyCool.h b/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
index 0884e72140e7e..ba93df8b03e61 100644
--- a/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
+++ b/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
@@ -40,6 +40,9 @@
 // See http://www.gccxml.org/Bug/bug.php?op=show&bugid=895
 // See also SealBase/DebugAids.h:83 (NDEBUG is defined as 1 else problems)
 #ifdef _WIN32
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
 #define NDEBUG 1
 #include <assert.h>
 #endif