diff --git a/src/futil.c b/src/futil.c
index 8e61493c660edd3570095f0236709839387204e9..07e1c771f247a493b65cc052f783e99d0bda94ec 100644
--- a/src/futil.c
+++ b/src/futil.c
@@ -137,6 +137,7 @@ geom.umn.edu; email: software@geom.umn.edu. */
 
 #if defined(unix) || defined(__unix)
 # include <sys/time.h>
+# include <arpa/inet.h>		/* for htonl() */
 # ifndef NeXT
 #  include <unistd.h>
 # endif