diff --git a/tag.c b/tag.c
index f54ac3f..c069dcc 100644
--- a/tag.c
+++ b/tag.c
@@ -4,6 +4,7 @@
 #include "dwm.h"
 #include <regex.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <X11/Xutil.h>
 
 /* static */