diff --git a/src/gui.c b/src/gui.c
index 19b147f..a6737f9 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <stdlib.h>
 
 #include "gui.h"
 #include "util.h"