diff --git a/src/drivers/bus/pci.c b/src/drivers/bus/pci.c
index 06b36a770e..e6260ca6ca 100644
--- a/src/drivers/bus/pci.c
+++ b/src/drivers/bus/pci.c
@@ -143,29 +143,67 @@ static void pci_read_bases ( struct pci_device *pci ) {
  *
  * @v pci		PCI device
  *
- * Set device to be a busmaster in case BIOS neglected to do so.  Also
- * adjust PCI latency timer to a reasonable value, 32.
+ * Set device to be a bus master in case BIOS neglected to do so.  Enable
+ * both memory and I/O space access.  Also adjust PCI latency timer to a
+ * reasonable value, 32.
  */
 void adjust_pci_device ( struct pci_device *pci ) {
+	pci_enable_device ( pci,
+			    PCI_COMMAND_MASTER | PCI_COMMAND_MEM |
+			    PCI_COMMAND_IO,
+			    32 );
+}
+
+/**
+ * Enable PCI device
+ *
+ * @v pci		PCI device
+ * @v flags		PCI command flags to enable
+ * @v latency		Minimum desired PCI latency timer or 0 to not adjust it
+ * @ret old_flags	Original PCI command flags
+ *
+ * Enable device by setting bits in the command register in case BIOS neglected
+ * to do so.  Also optionally adjust the PCI latency timer.
+ */
+unsigned pci_enable_device ( struct pci_device *pci, unsigned flags,
+	                     unsigned char latency ) {
 	unsigned short new_command, pci_command;
 	unsigned char pci_latency;
 
 	pci_read_config_word ( pci, PCI_COMMAND, &pci_command );
-	new_command = ( pci_command | PCI_COMMAND_MASTER |
-			PCI_COMMAND_MEM | PCI_COMMAND_IO );
+	new_command = ( pci_command | flags );
 	if ( pci_command != new_command ) {
-		DBGC ( pci, PCI_FMT " device not enabled by BIOS! Updating "
+		DBGC ( pci, PCI_FMT " device not fully enabled by BIOS! Updating "
 		       "PCI command %04x->%04x\n",
 		       PCI_ARGS ( pci ), pci_command, new_command );
 		pci_write_config_word ( pci, PCI_COMMAND, new_command );
 	}
 
-	pci_read_config_byte ( pci, PCI_LATENCY_TIMER, &pci_latency);
-	if ( pci_latency < 32 ) {
-		DBGC ( pci, PCI_FMT " latency timer is unreasonably low at "
-		       "%d. Setting to 32.\n", PCI_ARGS ( pci ), pci_latency );
-		pci_write_config_byte ( pci, PCI_LATENCY_TIMER, 32);
+	if ( latency ) {
+		pci_read_config_byte ( pci, PCI_LATENCY_TIMER, &pci_latency );
+		if ( pci_latency < latency ) {
+			DBGC ( pci, PCI_FMT " latency timer is unreasonably low at "
+			       "%d. Setting to %d.\n", PCI_ARGS ( pci ),
+			       pci_latency, latency );
+			pci_write_config_byte ( pci, PCI_LATENCY_TIMER, latency );
+		}
 	}
+	return pci_command;
+}
+
+/**
+ * Restore PCI device
+ *
+ * @v pci		PCI device
+ * @v old_flags		Flags to restore, returned from pci_enable_device
+ *
+ * Restore the command register of a PCI device to state it had before we
+ * changed it.
+ */
+void pci_restore_device ( struct pci_device *pci, unsigned old_flags ) {
+	DBGC ( pci, PCI_FMT " restoring PCI command to %04x\n",
+	       PCI_ARGS ( pci ), old_flags );
+	pci_write_config_word ( pci, PCI_COMMAND, old_flags );
 }
 
 /**
diff --git a/src/drivers/bus/virtio-pci.c b/src/drivers/bus/virtio-pci.c
index 3311595fb2..cb7b5e1c04 100644
--- a/src/drivers/bus/virtio-pci.c
+++ b/src/drivers/bus/virtio-pci.c
@@ -387,6 +387,16 @@ int vpm_find_vqs(struct virtio_pci_modern_device *vdev,
         if (err) {
             goto err_map_notify;
         }
+
+        /* enable memory or I/O access if not already enabled */
+        switch (vq->notification.flags & VIRTIO_PCI_REGION_TYPE_MASK) {
+            case VIRTIO_PCI_REGION_PORT:
+                pci_enable_device(vdev->pci, PCI_COMMAND_IO, 0);
+                break;
+            case VIRTIO_PCI_REGION_MEMORY:
+                pci_enable_device(vdev->pci, PCI_COMMAND_MEM, 0);
+                break;
+        }
     }
 
     /* Select and activate all queues. Has to be done last: once we do
diff --git a/src/drivers/net/virtio-net.c b/src/drivers/net/virtio-net.c
index fe0fd4b860..5b15836d63 100644
--- a/src/drivers/net/virtio-net.c
+++ b/src/drivers/net/virtio-net.c
@@ -92,6 +92,9 @@ struct virtnet_nic {
 	/** 0 for legacy, 1 for virtio 1.0 */
 	int virtio_version;
 
+	/** Content of the command register before we initialized the device */
+	unsigned old_pci_command;
+
 	/** Virtio 1.0 device data */
 	struct virtio_pci_modern_device vdev;
 
@@ -463,7 +466,8 @@ static int virtnet_probe_legacy ( struct pci_device *pci ) {
 	       virtnet, pci->dev.name, ioaddr, pci->irq );
 
 	/* Enable PCI bus master and reset NIC */
-	adjust_pci_device ( pci );
+	virtnet->old_pci_command = pci_enable_device ( pci,
+		PCI_COMMAND_MASTER | PCI_COMMAND_IO, 0 );
 	vp_reset ( ioaddr );
 
 	/* Load MAC address */
@@ -487,11 +491,33 @@ static int virtnet_probe_legacy ( struct pci_device *pci ) {
 	unregister_netdev ( netdev );
  err_register_netdev:
 	vp_reset ( ioaddr );
+	pci_restore_device ( pci, virtnet->old_pci_command );
 	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 	return rc;
 }
 
+/**
+ * Determine if the device uses at least one region of the given type
+ *
+ * @v vdev	Virtio-net device data
+ * @v type	The region type to test
+ * @ret result	Non-zero if the type is used, zero otherwise
+ */
+static int virtnet_uses_region_type ( struct virtio_pci_modern_device *vdev,
+				      unsigned type ) {
+	if ( ( vdev->common.flags & VIRTIO_PCI_REGION_TYPE_MASK ) == type ) {
+		return 1;
+	}
+	if ( ( vdev->isr.flags & VIRTIO_PCI_REGION_TYPE_MASK ) == type ) {
+		return 1;
+	}
+	if ( ( vdev->device.flags & VIRTIO_PCI_REGION_TYPE_MASK ) == type ) {
+		return 1;
+	}
+	return 0;
+}
+
 /**
  * Probe PCI device, modern virtio 1.0
  *
@@ -504,6 +530,7 @@ static int virtnet_probe_modern ( struct pci_device *pci, int *found_dev ) {
 	struct virtnet_nic *virtnet;
 	u64 features;
 	int rc, common, isr, notify, config, device;
+	unsigned pci_command;
 
 	common = virtio_pci_find_capability ( pci, VIRTIO_PCI_CAP_COMMON_CFG );
 	if ( ! common ) {
@@ -562,7 +589,14 @@ static int virtnet_probe_modern ( struct pci_device *pci, int *found_dev ) {
 	}
 
 	/* Enable the PCI device */
-	adjust_pci_device ( pci );
+	pci_command = PCI_COMMAND_MASTER;
+	if ( virtnet_uses_region_type ( &virtnet->vdev, VIRTIO_PCI_REGION_PORT ) ) {
+		pci_command |= PCI_COMMAND_IO;
+	}
+	if ( virtnet_uses_region_type ( &virtnet->vdev, VIRTIO_PCI_REGION_MEMORY ) ) {
+		pci_command |= PCI_COMMAND_MEM;
+	}
+	virtnet->old_pci_command = pci_enable_device ( pci, pci_command, 0 );
 
 	/* Reset the device and set initial status bits */
 	vpm_reset ( &virtnet->vdev );
@@ -601,6 +635,7 @@ static int virtnet_probe_modern ( struct pci_device *pci, int *found_dev ) {
 err_register_netdev:
 err_mac_address:
 	vpm_reset ( &virtnet->vdev );
+	pci_restore_device ( pci, virtnet->old_pci_command );
 	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 
@@ -638,6 +673,8 @@ static void virtnet_remove ( struct pci_device *pci ) {
 	struct net_device *netdev = pci_get_drvdata ( pci );
 	struct virtnet_nic *virtnet = netdev->priv;
 
+	pci_restore_device ( pci, virtnet->old_pci_command );
+
 	virtio_pci_unmap_capability ( &virtnet->vdev.device );
 	virtio_pci_unmap_capability ( &virtnet->vdev.isr );
 	virtio_pci_unmap_capability ( &virtnet->vdev.common );
diff --git a/src/include/ipxe/pci.h b/src/include/ipxe/pci.h
index ddd8c8d1e2..d39d28a0f4 100644
--- a/src/include/ipxe/pci.h
+++ b/src/include/ipxe/pci.h
@@ -281,6 +281,9 @@ struct pci_driver {
 	PCI_SLOT ( (pci)->busdevfn ), PCI_FUNC ( (pci)->busdevfn )
 
 extern void adjust_pci_device ( struct pci_device *pci );
+extern unsigned pci_enable_device ( struct pci_device *pci, unsigned flags,
+				    unsigned char latency );
+extern void pci_restore_device ( struct pci_device *pci, unsigned old_flags );
 extern unsigned long pci_bar_start ( struct pci_device *pci,
 				     unsigned int reg );
 extern int pci_read_config ( struct pci_device *pci );