diff --git a/runtime/mercury_runtime_util.c b/runtime/mercury_runtime_util.c
index 5e9b55756..301d45d54 100644
--- a/runtime/mercury_runtime_util.c
+++ b/runtime/mercury_runtime_util.c
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2001 The University of Melbourne.
+** Copyright (C) 2001-2002 The University of Melbourne.
 ** This file may only be copied under the terms of the GNU Library General
 ** Public License - see the file COPYING.LIB in the Mercury distribution.
 */
@@ -14,7 +14,11 @@
 #include	"mercury_runtime_util.h"
 
 #include	<stdio.h>
-#include	<unistd.h>
+
+#ifdef MR_HAVE_UNISTD_H
+  #include	<unistd.h>
+#endif
+
 #include	<errno.h>
 
 #ifndef MR_HAVE_STRERROR