diff --git a/libstdc++-v3/testsuite/17_intro/names_fortify.cc b/libstdc++-v3/testsuite/17_intro/names_fortify.cc
index c975412074b..f24af21f8a7 100644
--- a/libstdc++-v3/testsuite/17_intro/names_fortify.cc
+++ b/libstdc++-v3/testsuite/17_intro/names_fortify.cc
@@ -1,6 +1,7 @@
 // { dg-do compile { target *-*-linux* } }
 // { dg-add-options no_pch }
 
+#undef _FORTIFY_SOURCE
 #define _FORTIFY_SOURCE 2
 // Now we can define the macros to poison uses of non-reserved names:
 #include "names.cc"