Index: usr.sbin/bhyve/pci_nvme.c
===================================================================
--- usr.sbin/bhyve/pci_nvme.c
+++ usr.sbin/bhyve/pci_nvme.c
@@ -85,6 +85,9 @@
 
 #define	NVME_IOSLOTS		8
 
+/* The NVMe spec defines bits 13:4 in BAR0 as reserved */
+#define NVME_MMIO_SPACE_MIN	(1 << 14)
+
 #define	NVME_QUEUES		16
 #define	NVME_MAX_QENTRIES	2048
 
@@ -1847,9 +1850,18 @@
 	pci_set_cfgdata8(pi, PCIR_PROGIF,
 	                 PCIP_STORAGE_NVM_ENTERPRISE_NVMHCI_1_0);
 
-	/* allocate size of nvme registers + doorbell space for all queues */
-	pci_membar_sz = sizeof(struct nvme_registers) +
-	                2*sizeof(uint32_t)*(sc->max_queues + 1);
+	/*
+	 * Allocate size of NVMe registers + doorbell space for all queues.
+	 *
+	 * Note that the specification defines bits 13:4 as reserved
+	 * (i.e. 0). Most operating systems do not enforce this requirement,
+	 * but Windows appears to check this and will refuse to start the
+	 * device if these bits are set.
+	 */
+	pci_membar_sz = MAX(
+			sizeof(struct nvme_registers) +
+				2 * sizeof(uint32_t) * (sc->max_queues + 1),
+			NVME_MMIO_SPACE_MIN);
 
 	DPRINTF(("nvme membar size: %u\r\n", pci_membar_sz));