Index: sys/dev/pci/pci.c
===================================================================
--- sys/dev/pci/pci.c
+++ sys/dev/pci/pci.c
@@ -5000,6 +5000,7 @@
 	struct resource_list *rl = &dinfo->resources;
 	struct resource *res;
 	struct pci_map *pm;
+	uint16_t cmd;
 	pci_addr_t map, testval;
 	int mapsize;
 
@@ -5089,8 +5090,17 @@
 		device_printf(child,
 		    "Lazy allocation of %#jx bytes rid %#x type %d at %#jx\n",
 		    count, *rid, type, rman_get_start(res));
+
+	/* Disable decoding via the CMD register before updating the BAR */
+	cmd = pci_read_config(child, PCIR_COMMAND, 2);
+	pci_write_config(child, PCIR_COMMAND,
+	    cmd & ~(PCI_BAR_MEM(map) ? PCIM_CMD_MEMEN : PCIM_CMD_PORTEN), 2);
+
 	map = rman_get_start(res);
 	pci_write_bar(child, pm, map);
+
+	/* Restore the original value of the CMD register */
+	pci_write_config(child, PCIR_COMMAND, cmd, 2);
 out:
 	return (res);
 }