diff --git a/sys/dev/virtio/network/virtio_net.h b/sys/dev/virtio/network/virtio_net.h
--- a/sys/dev/virtio/network/virtio_net.h
+++ b/sys/dev/virtio/network/virtio_net.h
@@ -407,6 +407,32 @@
 	return (error);
 }
 
+/*
+ * For an outgoing packet, set the transmission csum flags if, according
+ * to the virtio-net header flag, the packet still needs a valid checksum.
+ */
+static inline int
+virtio_net_tx_txcsum(struct mbuf *m, struct virtio_net_hdr *hdr)
+{
+	if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+		switch (hdr->csum_offset) {
+		case offsetof(struct udphdr, uh_sum):
+			m->m_pkthdr.csum_flags |= CSUM_IP_UDP | CSUM_PSEUDO_HDR;
+			break;
+		case offsetof(struct tcphdr, th_sum):
+			m->m_pkthdr.csum_flags |= CSUM_IP_TCP | CSUM_PSEUDO_HDR;
+			break;
+		default:
+			/* A packet other than TCP or UDP is unexpected here */
+			return (1);
+		}
+	}
+
+	m->m_pkthdr.csum_data = hdr->csum_offset;
+
+	return (0);
+}
+
 static inline int
 virtio_net_tx_offload_ctx(struct mbuf *m, int *etype, int *proto, int *start)
 {
diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -2896,6 +2896,15 @@
 		}							\
 		if ((iface) != bifp)					\
 			ETHER_BPF_MTAP(iface, m);			\
+		if (m->m_pkthdr.csum_flags & (CSUM_IP_TCP | CSUM_IP_UDP)) { \
+			/* Incoming pkt that still needs csum calc. */	\
+			/* Probably from a software interface. */	\
+			/* In this case, we don't need the csum. */	\
+			m->m_pkthdr.csum_flags &= ~(CSUM_IP_TCP | CSUM_IP_UDP);\
+			m->m_pkthdr.csum_flags |= CSUM_DATA_VALID 	\
+			    | CSUM_PSEUDO_HDR;				\
+			m->m_pkthdr.csum_data = 0xFFFF;			\
+		}							\
 		/* Pass tagged packets to if_vlan, if it's loaded */	\
 		if (VLANTAGOF(m) != 0) {				\
 			if (bifp->if_vlantrunk == NULL) {		\
diff --git a/sys/net/if_tuntap.c b/sys/net/if_tuntap.c
--- a/sys/net/if_tuntap.c
+++ b/sys/net/if_tuntap.c
@@ -1781,9 +1781,21 @@
 	}
 
 	if (vhdr != NULL) {
-		if (virtio_net_rx_csum(m, &vhdr->hdr)) {
-			m_freem(m);
-			return (0);
+		if (ifp->if_bridge == NULL) {
+			if (virtio_net_rx_csum(m, &vhdr->hdr)) {
+				m_freem(m);
+				return (0);
+			}
+		} else {
+			/*
+			 * The tap interface is a bridge member. Most likely it
+			 * will be forwarded out over another interface. Thus,
+			 * setting transmission offload flags in the mbuf here.
+			 */
+			if (virtio_net_tx_txcsum(m, &vhdr->hdr)) {
+				m_freem(m);
+				return (0);
+			}
 		}
 	} else {
 		switch (ntohs(eh->ether_type)) {