diff --git a/ext/standard/string.c b/ext/standard/string.c
index 61fb9db4aa1..7d1b3a59852 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -31,6 +31,7 @@
 # include <locale.h>
 #endif
 #ifdef HAVE_LANGINFO_H
+#define __USE_GNU
 # include <langinfo.h>
 #endif
 #include "scanf.h"