diff --git a/src/os_unix.h b/src/os_unix.h
index 02eeafc..44c331c 100644
--- a/src/os_unix.h
+++ b/src/os_unix.h
@@ -225,6 +225,8 @@
 # include <starlet.h>
 # include <socket.h>
 # include <lib$routines.h>
+# include <libdef.h>
+# include <libdtdef.h>
 
 # ifdef FEAT_GUI_GTK
 #  include "gui_gtk_vms.h"