diff --git a/sys/net/if.h b/sys/net/if.h
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -160,7 +160,7 @@
 #define	IFF_STICKYARP	0x100000	/* (n) sticky ARP */
 #define	IFF_DYING	0x200000	/* (n) interface is winding down */
 #define	IFF_RENAMING	0x400000	/* (n) interface is being renamed */
-#define	IFF_SPARE	0x800000
+#define	IFF_PALLMULTI	0x800000	/* (n) user-requested allmulti mode */
 #define	IFF_NETLINK_1	0x1000000	/* (n) used by netlink */
 
 /*
diff --git a/sys/net/if.c b/sys/net/if.c
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -2611,7 +2611,12 @@
 		    (ifp->if_flags & IFF_UP) == 0) {
 			do_ifup = 1;
 		}
-		/* See if permanently promiscuous mode bit is about to flip */
+
+		/*
+		 * See if the promiscuous mode or allmulti bits are about to
+		 * flip.  They require special handling because in-kernel
+		 * consumers increment a counter when toggling them.
+		 */
 		if ((ifp->if_flags ^ new_flags) & IFF_PPROMISC) {
 			if (new_flags & IFF_PPROMISC)
 				ifp->if_flags |= IFF_PROMISC;
@@ -2622,6 +2627,12 @@
                                     ((new_flags & IFF_PPROMISC) ?
                                      "enabled" : "disabled"));
 		}
+		if ((ifp->if_flags ^ new_flags) & IFF_PALLMULTI) {
+			if (new_flags & IFF_PALLMULTI)
+				ifp->if_flags |= IFF_ALLMULTI;
+			else if (ifp->if_amcount == 0)
+				ifp->if_flags &= ~IFF_ALLMULTI;
+		}
 		ifp->if_flags = (ifp->if_flags & IFF_CANTCHANGE) |
 			(new_flags &~ IFF_CANTCHANGE);
 		if (ifp->if_ioctl) {
@@ -3383,7 +3394,8 @@
 if_allmulti(struct ifnet *ifp, int onswitch)
 {
 
-	return (if_setflag(ifp, IFF_ALLMULTI, 0, &ifp->if_amcount, onswitch));
+	return (if_setflag(ifp, IFF_ALLMULTI, IFF_PALLMULTI, &ifp->if_amcount,
+	    onswitch));
 }
 
 struct ifmultiaddr *