diff --git a/sys/dev/pci/pci_pci.c b/sys/dev/pci/pci_pci.c
index 6ef04251cd74..b3f82acfe350 100644
--- a/sys/dev/pci/pci_pci.c
+++ b/sys/dev/pci/pci_pci.c
@@ -436,6 +436,15 @@ pcib_alloc_window(struct pcib_softc *sc, struct pcib_window *w, int type,
 	if (!pcib_is_window_open(w))
 		return;
 
+#ifndef __PCI_BAR_ZERO_VALID
+	if (w->base == 0) {
+		w->base = max_address;
+		w->limit = 0;
+		pcib_write_windows(sc, w->mask);
+		return;
+	}
+#endif
+
 	if (w->base > max_address || w->limit > max_address) {
 		device_printf(sc->dev,
 		    "initial %s window has too many bits, ignoring\n", w->name);