--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -191,20 +191,42 @@ static int filter_nlmsg(struct nlmsghdr *n, struct rtattr **tb, int host_len)
 		return 0;
 	if ((filter.tos^r->rtm_tos)&filter.tosmask)
 		return 0;
-	if (filter.rdst.family &&
-	    (r->rtm_family != filter.rdst.family || filter.rdst.bitlen > r->rtm_dst_len))
-		return 0;
+	if (filter.rdst.family) {
+		if (r->rtm_family != filter.rdst.family ||
+		    filter.rdst.bitlen > r->rtm_dst_len)
+			return 0;
+	} else if (filter.rdst.flags & PREFIXLEN_SPECIFIED) {
+		if (filter.rdst.bitlen > r->rtm_dst_len)
+			return 0;
+	}
-	if (filter.mdst.family &&
-	    (r->rtm_family != filter.mdst.family ||
-	     (filter.mdst.bitlen >= 0 && filter.mdst.bitlen < r->rtm_dst_len)))
-		return 0;
+	if (filter.mdst.family) {
+		if (r->rtm_family != filter.mdst.family ||
+		    (filter.mdst.bitlen >= 0 &&
+		     filter.mdst.bitlen < r->rtm_dst_len))
+			return 0;
+	} else if (filter.mdst.flags & PREFIXLEN_SPECIFIED) {
+		if (filter.mdst.bitlen >= 0 &&
+		    filter.mdst.bitlen < r->rtm_dst_len)
+			return 0;
+	}
-	if (filter.rsrc.family &&
-	    (r->rtm_family != filter.rsrc.family || filter.rsrc.bitlen > r->rtm_src_len))
-		return 0;
+	if (filter.rsrc.family) {
+		if (r->rtm_family != filter.rsrc.family ||
+		    filter.rsrc.bitlen > r->rtm_src_len)
+			return 0;
+	} else if (filter.rsrc.flags & PREFIXLEN_SPECIFIED) {
+		if (filter.rsrc.bitlen > r->rtm_src_len)
+			return 0;
+	}
-	if (filter.msrc.family &&
-	    (r->rtm_family != filter.msrc.family ||
-	     (filter.msrc.bitlen >= 0 && filter.msrc.bitlen < r->rtm_src_len)))
-		return 0;
+	if (filter.msrc.family) {
+		if (r->rtm_family != filter.msrc.family ||
+		    (filter.msrc.bitlen >= 0 &&
+		     filter.msrc.bitlen < r->rtm_src_len))
+			return 0;
+	} else if (filter.msrc.flags & PREFIXLEN_SPECIFIED) {
+		if (filter.msrc.bitlen >= 0 &&
+		    filter.msrc.bitlen < r->rtm_src_len)
+			return 0;
+	}
 	if (filter.rvia.family) {
 		int family = r->rtm_family;
 
@@ -221,7 +243,9 @@ static int filter_nlmsg(struct nlmsghdr *n, struct rtattr **tb, int host_len)
 
 	if (tb[RTA_DST])
 		memcpy(&dst.data, RTA_DATA(tb[RTA_DST]), (r->rtm_dst_len+7)/8);
-	if (filter.rsrc.family || filter.msrc.family) {
+	if (filter.rsrc.family || filter.msrc.family ||
+	    filter.rsrc.flags & PREFIXLEN_SPECIFIED ||
+	    filter.msrc.flags & PREFIXLEN_SPECIFIED) {
 		if (tb[RTA_SRC])
 			memcpy(&src.data, RTA_DATA(tb[RTA_SRC]), (r->rtm_src_len+7)/8);
 	}
@@ -241,15 +265,18 @@ static int filter_nlmsg(struct nlmsghdr *n, struct rtattr **tb, int host_len)
 			memcpy(&prefsrc.data, RTA_DATA(tb[RTA_PREFSRC]), host_len/8);
 	}
 
-	if (filter.rdst.family && inet_addr_match(&dst, &filter.rdst, filter.rdst.bitlen))
+	if ((filter.rdst.family || filter.rdst.flags & PREFIXLEN_SPECIFIED) &&
+	    inet_addr_match(&dst, &filter.rdst, filter.rdst.bitlen))
 		return 0;
-	if (filter.mdst.family && filter.mdst.bitlen >= 0 &&
+	if ((filter.mdst.family || filter.mdst.flags & PREFIXLEN_SPECIFIED) &&
 	    inet_addr_match(&dst, &filter.mdst, r->rtm_dst_len))
 		return 0;
 
-	if (filter.rsrc.family && inet_addr_match(&src, &filter.rsrc, filter.rsrc.bitlen))
+	if ((filter.rsrc.family || filter.rsrc.flags & PREFIXLEN_SPECIFIED) &&
+	    inet_addr_match(&src, &filter.rsrc, filter.rsrc.bitlen))
 		return 0;
-	if (filter.msrc.family && filter.msrc.bitlen >= 0 &&
+	if ((filter.msrc.family || filter.msrc.flags & PREFIXLEN_SPECIFIED) &&
+	    filter.msrc.bitlen >= 0 &&
 	    inet_addr_match(&src, &filter.msrc, r->rtm_src_len))
 		return 0;
 
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -590,6 +590,7 @@ int get_prefix_1(inet_prefix *dst, char *arg, int family)
 		dst->family = family;
 		dst->bytelen = 0;
 		dst->bitlen = 0;
+		dst->flags |= PREFIXLEN_SPECIFIED;
 		return 0;
 	}