Index: /trunk/src/VBox/NetworkServices/NAT/pxping.c
===================================================================
--- /trunk/src/VBox/NetworkServices/NAT/pxping.c	(revision 49862)
+++ /trunk/src/VBox/NetworkServices/NAT/pxping.c	(revision 49863)
@@ -530,6 +530,10 @@
         IPH_OFFSET_SET(iph, ntohs(IPH_OFFSET(iph)));
         IPH_LEN_SET(iph, ntohs(IPH_LEN(iph)));
-#endif
+        /* wants checksum */
+        sum = inet_chksum_pbuf(p); /* sic(?) */
+        IPH_CHKSUM_SET(iph, sum);
+#else /* !RT_OS_DARWIN  */
         IPH_CHKSUM_SET(iph, 0); /* kernel will recalculate */
+#endif
     }
     else /* !pxping->hdrincl */