diff --git a/sys/net/if_sl.c b/sys/net/if_sl.c
index 621283b1a664..18e7f4085944 100644
--- a/sys/net/if_sl.c
+++ b/sys/net/if_sl.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if_sl.c	8.6 (Berkeley) 2/1/94
- * $Id: if_sl.c,v 1.37 1996/04/07 17:39:09 bde Exp $
+ * $Id: if_sl.c,v 1.38 1996/04/24 15:44:34 phk Exp $
  */
 
 /*
@@ -561,8 +561,8 @@ slstart(tp)
 			} while (m1 = m1->m_next);
 		}
 #endif
-		if ((ip = mtod(m, struct ip *))->ip_v == IPVERSION) &&
-		    (ip = mtod(m, struct ip *))->ip_p == IPPROTO_TCP) {
+		ip = mtod(m, struct ip *);
+		if (ip->ip_v == IPVERSION && ip->ip_p == IPPROTO_TCP) {
 			if (sc->sc_if.if_flags & SC_COMPRESS)
 				*mtod(m, u_char *) |= sl_compress_tcp(m, ip,
 				    &sc->sc_comp, 1);