diff -urNb old.nmap.rev/tcpip.cc new.nmap.rev/tcpip.cc
--- old.nmap.rev/tcpip.cc	Thu Feb 22 13:34:56 2007
+++ new.nmap.rev/tcpip.cc	Thu Feb 22 13:34:57 2007
@@ -913,6 +913,14 @@
     }
   } while (!pt);
 
+#ifdef OPENBSD
+#define BIOCIMMEDIATE   _IOW('B',112, u_int)
+  {
+    int v=1;
+    ioctl(pcap_get_selectable_fd(pt), BIOCIMMEDIATE, &v);
+  }
+#endif
+
 #ifdef WIN32
   /* We want any responses back ASAP */
    pcap_setmintocopy(pt, 1);