Index: head/sys/dev/hyperv/utilities/hv_heartbeat.c
===================================================================
--- head/sys/dev/hyperv/utilities/hv_heartbeat.c
+++ head/sys/dev/hyperv/utilities/hv_heartbeat.c
@@ -69,7 +69,7 @@
 	if (error)
 		return;
 
-	if (dlen < sizeof(struct vmbus_icmsg_hdr)) {
+	if (dlen < sizeof(*hdr)) {
 		device_printf(sc->ic_dev, "invalid data len %d\n", dlen);
 		return;
 	}