diff --git a/probe.c b/probe.c
index bb5ddd5..ba49bf8 100644
--- a/probe.c
+++ b/probe.c
@@ -173,13 +173,13 @@ static int is_openvpn_protocol (const char*p,ssize_t len, struct sslhcfg_protoco
          * whereas the packet id is increased with every transmitted datagram.
          */
 
-        if (len <= OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_128) + 4)
+        if (len <= OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_128) + sizeof(uint32_t))
             return PROBE_NEXT;
 
         if (ntohl(*(uint32_t*)(p + OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_128))) <= 5u)
             return PROBE_MATCH;
 
-        if (len <= OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_160) + 4)
+        if (len <= OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_160) + sizeof(uint32_t))
             return PROBE_NEXT;
 
         if (ntohl(*(uint32_t*)(p + OVPN_HARD_RESET_PACKET_ID_OFFSET(OVPN_HMAC_160))) <= 5u)