--- a/src/config.h.in
+++ b/src/config.h.in
@@ -32,6 +32,9 @@
 
 /* Define if you have the <sys/ioctl.h> header file.  */
 #undef HAVE_SYS_IOCTL_H
+
+/* Define if you have the <unistd.h> header file.  */
+#undef HAVE_UNISTD_H
 
 /* Define if you have the <winioctl.h> header file.  */
 #undef HAVE_WINIOCTL_H