Index: /trunk/src/VBox/NetworkServices/NAT/pxping.c
===================================================================
--- /trunk/src/VBox/NetworkServices/NAT/pxping.c	(revision 51699)
+++ /trunk/src/VBox/NetworkServices/NAT/pxping.c	(revision 51700)
@@ -1450,4 +1450,8 @@
 
     /* rewrite inner IP header */
+#if defined(RT_OS_DARWIN)
+    /* darwin converts inner length to host byte order too */
+    IPH_LEN_SET(oiph, htons(IPH_LEN(oiph)));
+#endif
     sum = (u16_t)~IPH_CHKSUM(oiph);
     sum += chksum_update_32((u32_t *)&oiph->src, ip4_addr_get_u32(&guest_ip));