Index: sys/dev/pci/pci.c
===================================================================
--- sys/dev/pci/pci.c	(revision 362147)
+++ sys/dev/pci/pci.c	(working copy)
@@ -5303,6 +5303,20 @@
 		/* This is a BAR that we failed to allocate earlier. */
 		mapsize = pm->pm_size;
 		map = pm->pm_value;
+
+#ifndef __PCI_BAR_ZERO_VALID
+		/*
+		 * Workaround for IO when booting without a system BIOS.
+		 *
+		 * IO port 0 is illegal on most PCI controllers and will
+		 * malfunction if assigned to a device.
+		 *
+		 * Ensure we can never allocate IO port 0.
+		 */
+		if (map == 0x00000001 && start == 0) {
+			start = 1;
+		}
+#endif
 	} else {
 		/*
 		 * Weed out the bogons, and figure out how large the