diff --git a/src/ui/interface.cpp b/src/ui/interface.cpp
index 28a505fbd..651afd98f 100644
--- a/src/ui/interface.cpp
+++ b/src/ui/interface.cpp
@@ -30,6 +30,7 @@
 ----------------------------------------------------------------------------*/
 
 #include <stdio.h>
+#include <stdlib.h>
 
 #include "freecraft.h"
 #include "video.h"