diff --git a/usr.sbin/bhyve/pci_ahci.c b/usr.sbin/bhyve/pci_ahci.c
--- a/usr.sbin/bhyve/pci_ahci.c
+++ b/usr.sbin/bhyve/pci_ahci.c
@@ -2422,7 +2422,7 @@
 static int
 pci_ahci_init(struct vmctx *ctx __unused, struct pci_devinst *pi, nvlist_t *nvl)
 {
-	char bident[sizeof("XX:XX:XX")];
+	char bident[sizeof("XXX:XXX:XXX")];
 	char node_name[sizeof("XX")];
 	struct blockif_ctxt *bctxt;
 	struct pci_ahci_softc *sc;
@@ -2469,7 +2469,7 @@
 		 * Attempt to open the backing image. Use the PCI slot/func
 		 * and the port number for the identifier string.
 		 */
-		snprintf(bident, sizeof(bident), "%d:%d:%d", pi->pi_slot,
+		snprintf(bident, sizeof(bident), "%u:%u:%u", pi->pi_slot,
 		    pi->pi_func, p);
 
 		bctxt = blockif_open(port_nvl, bident);
diff --git a/usr.sbin/bhyve/pci_nvme.c b/usr.sbin/bhyve/pci_nvme.c
--- a/usr.sbin/bhyve/pci_nvme.c
+++ b/usr.sbin/bhyve/pci_nvme.c
@@ -3152,7 +3152,7 @@
 static int
 pci_nvme_parse_config(struct pci_nvme_softc *sc, nvlist_t *nvl)
 {
-	char bident[sizeof("XX:X:X")];
+	char bident[sizeof("XXX:XXX")];
 	const char *value;
 	uint32_t sectsz;
 
@@ -3226,7 +3226,7 @@
 			return (-1);
 		}
 	} else {
-		snprintf(bident, sizeof(bident), "%d:%d",
+		snprintf(bident, sizeof(bident), "%u:%u",
 		    sc->nsc_pi->pi_slot, sc->nsc_pi->pi_func);
 		sc->nvstore.ctx = blockif_open(nvl, bident);
 		if (sc->nvstore.ctx == NULL) {
diff --git a/usr.sbin/bhyve/pci_virtio_block.c b/usr.sbin/bhyve/pci_virtio_block.c
--- a/usr.sbin/bhyve/pci_virtio_block.c
+++ b/usr.sbin/bhyve/pci_virtio_block.c
@@ -453,7 +453,7 @@
 pci_vtblk_init(struct vmctx *ctx __unused, struct pci_devinst *pi,
     nvlist_t *nvl)
 {
-	char bident[sizeof("XX:X:X")];
+	char bident[sizeof("XXX:XXX")];
 	struct blockif_ctxt *bctxt;
 	const char *path, *serial;
 	MD5_CTX mdctx;
@@ -465,7 +465,7 @@
 	/*
 	 * The supplied backing file has to exist
 	 */
-	snprintf(bident, sizeof(bident), "%d:%d", pi->pi_slot, pi->pi_func);
+	snprintf(bident, sizeof(bident), "%u:%u", pi->pi_slot, pi->pi_func);
 	bctxt = blockif_open(nvl, bident);
 	if (bctxt == NULL) {
 		perror("Could not open backing file");