diff --git a/cmd-kill-session.c b/cmd-kill-session.c
index 22c37b2c..4bf36d78 100644
--- a/cmd-kill-session.c
+++ b/cmd-kill-session.c
@@ -18,6 +18,8 @@
 
 #include <sys/types.h>
 
+#include <stdlib.h>
+
 #include "tmux.h"
 
 /*
diff --git a/cmd-kill-window.c b/cmd-kill-window.c
index 4353c1c1..0253605f 100644
--- a/cmd-kill-window.c
+++ b/cmd-kill-window.c
@@ -18,6 +18,8 @@
 
 #include <sys/types.h>
 
+#include <stdlib.h>
+
 #include "tmux.h"
 
 /*