diff --git a/osscan2.cc b/osscan2.cc
index 702117dde..a05d54c36 100644
--- a/osscan2.cc
+++ b/osscan2.cc
@@ -2303,7 +2303,7 @@ bool HostOsScan::processT1_7Resp(HostOsScanStats *hss, struct ip *ip, int replyN
 
   /* Next we check whether the Don't Fragment bit is set */
   AVs[current_testno].attribute = (char*)"DF";
-  if(ntohs(ip->ip_off) & 0x4000) {
+  if(ntohs(ip->ip_off) & IP_DF) {
     strcpy(AVs[current_testno].value,"Y");
   } else strcpy(AVs[current_testno].value, "N");
 
@@ -2486,7 +2486,7 @@ bool HostOsScan::processTUdpResp(HostOsScanStats *hss, struct ip *ip) {
 
   /* Now let us do an easy one, Don't fragment */
   AVs[current_testno].attribute = (char*)"DF";
-  if(ntohs(ip->ip_off) & 0x4000) {
+  if(ntohs(ip->ip_off) & IP_DF) {
     strcpy(AVs[current_testno].value,"Y");
   } else strcpy(AVs[current_testno].value, "N");
 
diff --git a/tcpip.cc b/tcpip.cc
index 4cb567c9c..f3eca192d 100644
--- a/tcpip.cc
+++ b/tcpip.cc
@@ -448,7 +448,7 @@ static const char *ippackethdrinfo(const u8 *packet, u32 len) {
   inet_ntop(AF_INET, &saddr, srchost, sizeof(srchost));
   inet_ntop(AF_INET, &daddr, dsthost, sizeof(dsthost));
 
-  frag_off = 8 * (ntohs(ip->ip_off) & 8191) /* 2^13 - 1 */;
+  frag_off = 8 * (ntohs(ip->ip_off) & IP_OFFMASK);
   more_fragments = ntohs(ip->ip_off) & IP_MF;
   if (frag_off || more_fragments) {
     Snprintf(fragnfo, sizeof(fragnfo), " frag offset=%d%s", frag_off, more_fragments ? "+" : "");
@@ -1591,7 +1591,7 @@ if (!packet) {
 
 bullshit.s_addr = ip->ip_src.s_addr; bullshit2.s_addr = ip->ip_dst.s_addr;
 /* this is gay */
-realfrag = htons(ntohs(ip->ip_off) & 8191 /* 2^13 - 1 */);
+realfrag = htons(ntohs(ip->ip_off) & IP_OFFMASK);
 tot_len = htons(ip->ip_len);
 strncpy(sourcehost, inet_ntoa(bullshit), 16);
 i =  4 * (ntohs(ip->ip_hl) + ntohs(tcp->th_off));
@@ -1650,7 +1650,7 @@ if (!packet) {
 
 bullshit.s_addr = ip->ip_src.s_addr; bullshit2.s_addr = ip->ip_dst.s_addr;
 /* this is gay */
-realfrag = htons(ntohs(ip->ip_off) & 8191 /* 2^13 - 1 */);
+realfrag = htons(ntohs(ip->ip_off) & IP_OFFMASK);
 tot_len = htons(ip->ip_len);
 strncpy(sourcehost, inet_ntoa(bullshit), 16);
 i =  4 * (ntohs(ip->ip_hl)) + 8;