diff --git a/lib/mulk.c b/lib/mulk.c
index 9342032..21e5ccb 100644
--- a/lib/mulk.c
+++ b/lib/mulk.c
@@ -30,6 +30,7 @@
  * files in the program, then also delete it here.
  *---------------------------------------------------------------------------*/
 
+#include <locale.h>
 #include "m_malloc.h"
 #include "buffer_array.h"
 #include "url_list.h"