diff --git a/usr.sbin/bhyve/amd64/pci_gvt-d.c b/usr.sbin/bhyve/amd64/pci_gvt-d.c
--- a/usr.sbin/bhyve/amd64/pci_gvt-d.c
+++ b/usr.sbin/bhyve/amd64/pci_gvt-d.c
@@ -222,6 +222,13 @@
 	opregion->len = header->size * KB;
 	munmap(header, sizeof(*header));
 
+	if (opregion->len != sizeof(struct igd_opregion)) {
+		warnx("%s: Invalid OpRegion size of 0x%lx", __func__,
+		    opregion->len);
+		close(memfd);
+		return (-1);
+	}
+
 	opregion->hva = mmap(NULL, opregion->len, PROT_READ, MAP_SHARED, memfd,
 	    opregion->hpa);
 	if (opregion->hva == MAP_FAILED) {