Index: usr.sbin/bhyve/pci_virtio_net.c
===================================================================
--- usr.sbin/bhyve/pci_virtio_net.c
+++ usr.sbin/bhyve/pci_virtio_net.c
@@ -109,7 +109,6 @@
 	uint64_t	vsc_features;	/* negotiated features */
 	
 	pthread_mutex_t	rx_mtx;
-	unsigned int	rx_vhdrlen;
 	int		rx_merge;	/* merged rx bufs in use */
 
 	pthread_t 	tx_tid;
@@ -149,6 +148,16 @@
 	/* Acquire the RX lock to block RX processing. */
 	pthread_mutex_lock(&sc->rx_mtx);
 
+	/*
+	 * Make sure receive operation is disabled at least until we
+	 * re-negotiate the features, since receive operation depends
+	 * on the value of sc->rx_merge and the header length, which
+	 * are both set in pci_vtnet_neg_features().
+	 * Receive operation will be enabled again once the guest adds
+	 * the first receive buffers and kicks us.
+	 */
+	netbe_rx_disable(sc->vsc_be);
+
 	/* Set sc->resetting and give a chance to the TX thread to stop. */
 	pthread_mutex_lock(&sc->tx_mtx);
 	sc->resetting = 1;
@@ -158,9 +167,6 @@
 		pthread_mutex_lock(&sc->tx_mtx);
 	}
 
-	sc->rx_merge = 1;
-	sc->rx_vhdrlen = sizeof(struct virtio_net_rxhdr);
-
 	/*
 	 * Now reset rings, MSI-X vectors, and negotiated capabilities.
 	 * Do that with the TX lock held, since we need to reset
@@ -512,8 +518,7 @@
 
 	sc->resetting = 0;
 
-	sc->rx_merge = 1;
-	sc->rx_vhdrlen = sizeof(struct virtio_net_rxhdr);
+	sc->rx_merge = 0;
 	pthread_mutex_init(&sc->rx_mtx, NULL); 
 
 	/* 
@@ -568,18 +573,24 @@
 pci_vtnet_neg_features(void *vsc, uint64_t negotiated_features)
 {
 	struct pci_vtnet_softc *sc = vsc;
+	unsigned int rx_vhdrlen;
 
 	sc->vsc_features = negotiated_features;
 
-	if (!(negotiated_features & VIRTIO_NET_F_MRG_RXBUF)) {
+	if (negotiated_features & VIRTIO_NET_F_MRG_RXBUF) {
+		rx_vhdrlen = sizeof(struct virtio_net_rxhdr);
+		sc->rx_merge = 1;
+	} else {
+		/*
+		 * Without mergeable rx buffers, virtio-net header is 2
+		 * bytes shorter than sizeof(struct virtio_net_rxhdr).
+		 */
+		rx_vhdrlen = sizeof(struct virtio_net_rxhdr) - 2;
 		sc->rx_merge = 0;
-		/* Without mergeable rx buffers, virtio-net header is 2
-		 * bytes shorter than sizeof(struct virtio_net_rxhdr). */
-		sc->rx_vhdrlen = sizeof(struct virtio_net_rxhdr) - 2;
 	}
 
 	/* Tell the backend to enable some capabilities it has advertised. */
-	netbe_set_cap(sc->vsc_be, negotiated_features, sc->rx_vhdrlen);
+	netbe_set_cap(sc->vsc_be, negotiated_features, rx_vhdrlen);
 }
 
 static struct pci_devemu pci_de_vnet = {