Index: sys/dev/virtio/mmio/virtio_mmio.c
===================================================================
--- sys/dev/virtio/mmio/virtio_mmio.c
+++ sys/dev/virtio/mmio/virtio_mmio.c
@@ -88,6 +88,7 @@
 static void	vtmmio_set_status(device_t, uint8_t);
 static void	vtmmio_read_dev_config(device_t, bus_size_t, void *, int);
 static void	vtmmio_write_dev_config(device_t, bus_size_t, void *, int);
+static uint32_t	vtmmio_virtqueue_size(device_t dev, int idx);
 static void	vtmmio_describe_features(struct vtmmio_softc *, const char *,
 		    uint64_t);
 static void	vtmmio_probe_and_attach_child(struct vtmmio_softc *);
@@ -161,6 +162,7 @@
 	DEVMETHOD(virtio_bus_notify_vq,		  vtmmio_notify_virtqueue),
 	DEVMETHOD(virtio_bus_read_device_config,  vtmmio_read_dev_config),
 	DEVMETHOD(virtio_bus_write_device_config, vtmmio_write_dev_config),
+	DEVMETHOD(virtio_bus_virtqueue_size,	  vtmmio_virtqueue_size),
 
 	DEVMETHOD_END
 };
@@ -404,6 +406,19 @@
 	return ((sc->vtmmio_features & feature) != 0);
 }
 
+static uint32_t
+vtmmio_virtqueue_size(device_t dev, int idx)
+{
+	struct vtmmio_softc *sc;
+	uint32_t size;
+
+	sc = device_get_softc(dev);
+	vtmmio_select_virtqueue(sc, idx);
+	size = vtmmio_read_config_4(sc, VIRTIO_MMIO_QUEUE_NUM_MAX);
+
+	return (size);
+}
+
 static int
 vtmmio_alloc_virtqueues(device_t dev, int flags, int nvqs,
     struct vq_alloc_info *vq_info)
Index: sys/dev/virtio/pci/virtio_pci.c
===================================================================
--- sys/dev/virtio/pci/virtio_pci.c
+++ sys/dev/virtio/pci/virtio_pci.c
@@ -113,6 +113,7 @@
 
 static uint64_t	vtpci_negotiate_features(device_t, uint64_t);
 static int	vtpci_with_feature(device_t, uint64_t);
+static uint32_t	vtpci_virtqueue_size(device_t dev, int idx);
 static int	vtpci_alloc_virtqueues(device_t, int, int,
 		    struct vq_alloc_info *);
 static int	vtpci_setup_intr(device_t, enum intr_type);
@@ -215,6 +216,7 @@
 	DEVMETHOD(virtio_bus_notify_vq,		  vtpci_notify_virtqueue),
 	DEVMETHOD(virtio_bus_read_device_config,  vtpci_read_dev_config),
 	DEVMETHOD(virtio_bus_write_device_config, vtpci_write_dev_config),
+	DEVMETHOD(virtio_bus_virtqueue_size,	  vtpci_virtqueue_size),
 
 	DEVMETHOD_END
 };
@@ -474,6 +476,19 @@
 	return ((sc->vtpci_features & feature) != 0);
 }
 
+static uint32_t
+vtpci_virtqueue_size(device_t dev, int idx)
+{
+	struct vtpci_softc *sc;
+	uint32_t size;
+
+	sc = device_get_softc(dev);
+	vtpci_select_virtqueue(sc, idx);
+	size = vtpci_read_config_2(sc, VIRTIO_PCI_QUEUE_NUM);
+
+	return (size);
+}
+
 static int
 vtpci_alloc_virtqueues(device_t dev, int flags, int nvqs,
     struct vq_alloc_info *vq_info)
Index: sys/dev/virtio/scsi/virtio_scsi.c
===================================================================
--- sys/dev/virtio/scsi/virtio_scsi.c
+++ sys/dev/virtio/scsi/virtio_scsi.c
@@ -68,6 +68,8 @@
 
 #include "virtio_if.h"
 
+#define VTSCSI_FIRST_REQUEST_QUEUE	2
+
 static int	vtscsi_modevent(module_t, int, void *);
 
 static int	vtscsi_probe(device_t);
@@ -79,7 +81,8 @@
 static void	vtscsi_negotiate_features(struct vtscsi_softc *);
 static void	vtscsi_read_config(struct vtscsi_softc *,
 		    struct virtio_scsi_config *);
-static int	vtscsi_maximum_segments(struct vtscsi_softc *, int);
+static uint32_t	vtscsi_minimum_request_queue_size(struct vtscsi_softc *, int);
+static int	vtscsi_maximum_segments(struct vtscsi_softc *, int, int);
 static int	vtscsi_alloc_virtqueues(struct vtscsi_softc *);
 static void	vtscsi_write_device_config(struct vtscsi_softc *);
 static int	vtscsi_reinit(struct vtscsi_softc *);
@@ -297,7 +300,8 @@
 
 	vtscsi_write_device_config(sc);
 
-	sc->vtscsi_max_nsegs = vtscsi_maximum_segments(sc, scsicfg.seg_max);
+	sc->vtscsi_max_nsegs = vtscsi_maximum_segments(sc, scsicfg.seg_max,
+	    scsicfg.num_queues);
 	sc->vtscsi_sglist = sglist_alloc(sc->vtscsi_max_nsegs, M_NOWAIT);
 	if (sc->vtscsi_sglist == NULL) {
 		error = ENOMEM;
@@ -437,8 +441,27 @@
 
 #undef VTSCSI_GET_CONFIG
 
+static uint32_t
+vtscsi_minimum_request_queue_size(struct vtscsi_softc *sc, int num_queues)
+{
+	device_t dev;
+	uint32_t size, s;
+	int i;
+
+	dev = sc->vtscsi_dev;
+	size = 0;
+	for (i = 0; i < num_queues; ++i) {
+		s = virtio_virtqueue_size(dev, i + VTSCSI_FIRST_REQUEST_QUEUE);
+		if (s != 0 && (size == 0 || s < size)) {
+			size = s;
+		}
+	}
+
+	return (size);
+}
+
 static int
-vtscsi_maximum_segments(struct vtscsi_softc *sc, int seg_max)
+vtscsi_maximum_segments(struct vtscsi_softc *sc, int seg_max, int num_queues)
 {
 	int nsegs;
 
@@ -448,6 +471,12 @@
 		nsegs += MIN(seg_max, MAXPHYS / PAGE_SIZE + 1);
 		if (sc->vtscsi_flags & VTSCSI_FLAG_INDIRECT)
 			nsegs = MIN(nsegs, VIRTIO_MAX_INDIRECT);
+		/*
+		 * Ensure the assertions in virtqueue_enqueue(),
+		 * even if the hypervisor reports a bad seg_max.
+		 */
+		nsegs = MIN(nsegs,
+		    vtscsi_minimum_request_queue_size(sc, num_queues));
 	} else
 		nsegs += 1;
 
Index: sys/dev/virtio/virtio.h
===================================================================
--- sys/dev/virtio/virtio.h
+++ sys/dev/virtio/virtio.h
@@ -96,6 +96,7 @@
 int	 virtio_config_generation(device_t dev);
 int	 virtio_reinit(device_t dev, uint64_t features);
 void	 virtio_reinit_complete(device_t dev);
+uint32_t virtio_virtqueue_size(device_t dev, int idx);
 int	 virtio_child_pnpinfo_str(device_t busdev, device_t child, char *buf,
 	     size_t buflen);
 
Index: sys/dev/virtio/virtio.c
===================================================================
--- sys/dev/virtio/virtio.c
+++ sys/dev/virtio/virtio.c
@@ -287,6 +287,13 @@
 	return (0);
 }
 
+uint32_t
+virtio_virtqueue_size(device_t dev, int idx)
+{
+
+	return (VIRTIO_BUS_VIRTQUEUE_SIZE(device_get_parent(dev), idx));
+}
+
 static int
 virtio_modevent(module_t mod, int type, void *unused)
 {
Index: sys/dev/virtio/virtio_bus_if.m
===================================================================
--- sys/dev/virtio/virtio_bus_if.m
+++ sys/dev/virtio/virtio_bus_if.m
@@ -104,3 +104,7 @@
 	device_t	dev;
 };
 
+METHOD uint32_t virtqueue_size {
+	device_t	dev;
+	int			idx;
+};