diff --git a/sysdep/bsd/setkey.h b/sysdep/bsd/setkey.h
index b417faca..d0ec6620 100644
--- a/sysdep/bsd/setkey.h
+++ b/sysdep/bsd/setkey.h
@@ -63,7 +63,7 @@ setkey_send(struct sadb_msg *msg, uint len)
  * operations to implement replace.
  */
 static int
-setkey_md5(sockaddr *src, sockaddr *dst, char *passwd, uint type)
+setkey_md5(sockaddr *src, sockaddr *dst, uint pxlen, char *passwd, uint type)
 {
   uint passwd_len = passwd ? strlen(passwd) : 0;
 
@@ -122,7 +122,7 @@ setkey_md5(sockaddr *src, sockaddr *dst, char *passwd, uint type)
   saddr->sadb_address_len = PFKEY_UNIT64(len);
   saddr->sadb_address_exttype = SADB_EXT_ADDRESS_SRC;
   saddr->sadb_address_proto = IPSEC_ULPROTO_ANY;
-  saddr->sadb_address_prefixlen = MAX_PREFIX_LENGTH;
+  saddr->sadb_address_prefixlen = pxlen;
   memcpy(pos + sizeof(struct sadb_address), &src->sa, src->sa.sa_len);
   pos += len;
 
@@ -132,7 +132,7 @@ setkey_md5(sockaddr *src, sockaddr *dst, char *passwd, uint type)
   daddr->sadb_address_len = PFKEY_UNIT64(len);
   daddr->sadb_address_exttype = SADB_EXT_ADDRESS_DST;
   daddr->sadb_address_proto = IPSEC_ULPROTO_ANY;
-  daddr->sadb_address_prefixlen = MAX_PREFIX_LENGTH;
+  daddr->sadb_address_prefixlen = pxlen;
   memcpy(pos + sizeof(struct sadb_address), &dst->sa, dst->sa.sa_len);
   pos += len;
 
@@ -152,18 +152,20 @@ sk_set_md5_in_sasp_db(sock *s, ip_addr local, ip_addr remote, struct iface *ifa,
   sockaddr_fill(&src, s->af, local, ifa, 0);
   sockaddr_fill(&dst, s->af, remote, ifa, 0);
 
+  uint pxlen = (s->af == AF_INET) ? IP4_MAX_PREFIX_LENGTH : IP6_MAX_PREFIX_LENGTH;
+
   if (passwd && *passwd)
   {
     int len = strlen(passwd);
     if (len > TCP_KEYLEN_MAX)
       ERR_MSG("The password for TCP MD5 Signature is too long");
 
-    if (setkey_md5(&src, &dst, passwd, SADB_ADD) < 0)
+    if (setkey_md5(&src, &dst, pxlen, passwd, SADB_ADD) < 0)
       ERR_MSG("Cannot add TCP-MD5 password into the IPsec SA/SP database");
   }
   else
   {
-    if (setkey_md5(&src, &dst, NULL, SADB_DELETE) < 0)
+    if (setkey_md5(&src, &dst, pxlen, NULL, SADB_DELETE) < 0)
       ERR_MSG("Cannot delete TCP-MD5 password from the IPsec SA/SP database");
   }
   return 0;