diff --git a/simgear/io/sg_netChat.hxx b/simgear/io/sg_netChat.hxx
index 8c346728..abba2b68 100644
--- a/simgear/io/sg_netChat.hxx
+++ b/simgear/io/sg_netChat.hxx
@@ -62,6 +62,7 @@
 #define SG_NET_CHAT_H
 
 #include <memory>
+#include <cstdlib>
 #include <simgear/io/sg_netBuffer.hxx>
 
 namespace simgear