Index: head/lib/libvmmapi/vmmapi.h
===================================================================
--- head/lib/libvmmapi/vmmapi.h
+++ head/lib/libvmmapi/vmmapi.h
@@ -181,6 +181,7 @@
 int	vm_setup_pptdev_msix(struct vmctx *ctx, int vcpu, int bus, int slot,
 	    int func, int idx, uint64_t addr, uint64_t msg,
 	    uint32_t vector_control);
+int	vm_disable_pptdev_msix(struct vmctx *ctx, int bus, int slot, int func);
 
 int	vm_get_intinfo(struct vmctx *ctx, int vcpu, uint64_t *i1, uint64_t *i2);
 int	vm_set_intinfo(struct vmctx *ctx, int vcpu, uint64_t exit_intinfo);
Index: head/lib/libvmmapi/vmmapi.c
===================================================================
--- head/lib/libvmmapi/vmmapi.c
+++ head/lib/libvmmapi/vmmapi.c
@@ -1017,6 +1017,19 @@
 	return ioctl(ctx->fd, VM_PPTDEV_MSIX, &pptmsix);
 }
 
+int
+vm_disable_pptdev_msix(struct vmctx *ctx, int bus, int slot, int func)
+{
+	struct vm_pptdev ppt;
+
+	bzero(&ppt, sizeof(ppt));
+	ppt.bus = bus;
+	ppt.slot = slot;
+	ppt.func = func;
+
+	return ioctl(ctx->fd, VM_PPTDEV_DISABLE_MSIX, &ppt);
+}
+
 uint64_t *
 vm_get_stats(struct vmctx *ctx, int vcpu, struct timeval *ret_tv,
 	     int *ret_entries)
@@ -1641,7 +1654,8 @@
 	    VM_ISA_DEASSERT_IRQ, VM_ISA_PULSE_IRQ, VM_ISA_SET_IRQ_TRIGGER,
 	    VM_SET_CAPABILITY, VM_GET_CAPABILITY, VM_BIND_PPTDEV,
 	    VM_UNBIND_PPTDEV, VM_MAP_PPTDEV_MMIO, VM_PPTDEV_MSI,
-	    VM_PPTDEV_MSIX, VM_INJECT_NMI, VM_STATS, VM_STAT_DESC,
+	    VM_PPTDEV_MSIX, VM_PPTDEV_DISABLE_MSIX,
+	    VM_INJECT_NMI, VM_STATS, VM_STAT_DESC,
 	    VM_SET_X2APIC_STATE, VM_GET_X2APIC_STATE,
 	    VM_GET_HPET_CAPABILITIES, VM_GET_GPA_PMAP, VM_GLA2GPA,
 	    VM_GLA2GPA_NOFAULT,
Index: head/sys/amd64/include/vmm_dev.h
===================================================================
--- head/sys/amd64/include/vmm_dev.h
+++ head/sys/amd64/include/vmm_dev.h
@@ -301,6 +301,7 @@
 	IOCNUM_MAP_PPTDEV_MMIO = 42,
 	IOCNUM_PPTDEV_MSI = 43,
 	IOCNUM_PPTDEV_MSIX = 44,
+	IOCNUM_PPTDEV_DISABLE_MSIX = 45,
 
 	/* statistics */
 	IOCNUM_VM_STATS = 50, 
@@ -413,6 +414,8 @@
 	_IOW('v', IOCNUM_PPTDEV_MSI, struct vm_pptdev_msi)
 #define	VM_PPTDEV_MSIX \
 	_IOW('v', IOCNUM_PPTDEV_MSIX, struct vm_pptdev_msix)
+#define	VM_PPTDEV_DISABLE_MSIX \
+	_IOW('v', IOCNUM_PPTDEV_DISABLE_MSIX, struct vm_pptdev)
 #define VM_INJECT_NMI \
 	_IOW('v', IOCNUM_INJECT_NMI, struct vm_nmi)
 #define	VM_STATS \
Index: head/sys/amd64/vmm/io/ppt.h
===================================================================
--- head/sys/amd64/vmm/io/ppt.h
+++ head/sys/amd64/vmm/io/ppt.h
@@ -38,6 +38,7 @@
 		      uint64_t addr, uint64_t msg, int numvec);
 int	ppt_setup_msix(struct vm *vm, int vcpu, int bus, int slot, int func,
 		int idx, uint64_t addr, uint64_t msg, uint32_t vector_control);
+int	ppt_disable_msix(struct vm *vm, int bus, int slot, int func);
 int	ppt_assigned_devices(struct vm *vm);
 bool	ppt_is_mmio(struct vm *vm, vm_paddr_t gpa);
 
Index: head/sys/amd64/vmm/io/ppt.c
===================================================================
--- head/sys/amd64/vmm/io/ppt.c
+++ head/sys/amd64/vmm/io/ppt.c
@@ -518,6 +518,10 @@
 	if (ppt->vm != vm)		/* Make sure we own this device */
 		return (EBUSY);
 
+	/* Reject attempts to enable MSI while MSI-X is active. */
+	if (ppt->msix.num_msgs != 0 && numvec != 0)
+		return (EBUSY);
+
 	/* Free any allocated resources */
 	ppt_teardown_msi(ppt);
 
@@ -607,6 +611,10 @@
 	if (ppt->vm != vm)		/* Make sure we own this device */
 		return (EBUSY);
 
+	/* Reject attempts to enable MSI-X while MSI is active. */
+	if (ppt->msi.num_msgs != 0)
+		return (EBUSY);
+
 	dinfo = device_get_ivars(ppt->dev);
 	if (!dinfo) 
 		return (ENXIO);
@@ -698,5 +706,20 @@
 		ppt_teardown_msix_intr(ppt, idx);
 	}
 
+	return (0);
+}
+
+int
+ppt_disable_msix(struct vm *vm, int bus, int slot, int func)
+{
+	struct pptdev *ppt;
+
+	ppt = ppt_find(bus, slot, func);
+	if (ppt == NULL)
+		return (ENOENT);
+	if (ppt->vm != vm)		/* Make sure we own this device */
+		return (EBUSY);
+
+	ppt_teardown_msix(ppt);
 	return (0);
 }
Index: head/sys/amd64/vmm/vmm_dev.c
===================================================================
--- head/sys/amd64/vmm/vmm_dev.c
+++ head/sys/amd64/vmm/vmm_dev.c
@@ -514,6 +514,11 @@
 				       pptmsix->addr, pptmsix->msg,
 				       pptmsix->vector_control);
 		break;
+	case VM_PPTDEV_DISABLE_MSIX:
+		pptdev = (struct vm_pptdev *)data;
+		error = ppt_disable_msix(sc->vm, pptdev->bus, pptdev->slot,
+					 pptdev->func);
+		break;
 	case VM_MAP_PPTDEV_MMIO:
 		pptmmio = (struct vm_pptdev_mmio *)data;
 		error = ppt_map_mmio(sc->vm, pptmmio->bus, pptmmio->slot,
Index: head/usr.sbin/bhyve/pci_passthru.c
===================================================================
--- head/usr.sbin/bhyve/pci_passthru.c
+++ head/usr.sbin/bhyve/pci_passthru.c
@@ -869,6 +869,11 @@
 				if (error)
 					err(1, "vm_setup_pptdev_msix");
 			}
+		} else {
+			error = vm_disable_pptdev_msix(ctx, sc->psc_sel.pc_bus,
+			    sc->psc_sel.pc_dev, sc->psc_sel.pc_func);
+			if (error)
+				err(1, "vm_disable_pptdev_msix");
 		}
 		return (0);
 	}