diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 9a5c9f0..6570f379 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -401,6 +401,21 @@
 		pfx->s6_addr[o] = addr->s6_addr[o] & (0xff00 >> b);
 }
 
+static inline void ipv6_addr_prefix_copy(struct in6_addr *addr,
+					 const struct in6_addr *pfx,
+					 int plen)
+{
+	/* caller must guarantee 0 <= plen <= 128 */
+	int o = plen >> 3,
+	    b = plen & 0x7;
+
+	memcpy(addr->s6_addr, pfx, o);
+	if (b != 0) {
+		addr->s6_addr[o] &= ~(0xff00 >> b);
+		addr->s6_addr[o] |= (pfx->s6_addr[o] & (0xff00 >> b));
+	}
+}
+
 static inline void __ipv6_addr_set_half(__be32 *addr,
 					__be32 wh, __be32 wl)
 {