diff --git a/sys/arch/i386/i386/mainbus.c b/sys/arch/i386/i386/mainbus.c
index 15f3781838a9..2f232085a458 100644
--- a/sys/arch/i386/i386/mainbus.c
+++ b/sys/arch/i386/i386/mainbus.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: mainbus.c,v 1.15 1996/11/22 00:19:08 jtk Exp $	*/
+/*	$NetBSD: mainbus.c,v 1.16 1996/11/28 02:43:58 thorpej Exp $	*/
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All rights reserved.
@@ -73,6 +73,12 @@ union mainbus_attach_args {
 #endif
 };
 
+/*
+ * This is set when the ISA bus is attached.  If it's not set by the
+ * time it's checked below, then mainbus attempts to attach an ISA.
+ */
+int	isa_has_been_seen;
+
 /*
  * Probe for the mainbus; always succeeds.
  */
@@ -120,7 +126,7 @@ mainbus_attach(parent, self, aux)
 		config_found(self, &mba.mba_eba, mainbus_print);
 	}
 
-	if (1 /* XXX ISA NOT YET SEEN */) {
+	if (isa_has_been_seen == 0) {
 		mba.mba_iba.iba_busname = "isa";
 		mba.mba_iba.iba_iot = I386_BUS_SPACE_IO;
 		mba.mba_iba.iba_memt = I386_BUS_SPACE_MEM;
diff --git a/sys/arch/i386/isa/isa_machdep.c b/sys/arch/i386/isa/isa_machdep.c
index 78c1e38cd47c..aae612fde872 100644
--- a/sys/arch/i386/isa/isa_machdep.c
+++ b/sys/arch/i386/isa/isa_machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: isa_machdep.c,v 1.16 1996/11/20 14:09:07 mycroft Exp $	*/
+/*	$NetBSD: isa_machdep.c,v 1.17 1996/11/28 02:43:53 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1993, 1994, 1996 Charles M. Hannum.  All rights reserved.
@@ -333,6 +333,13 @@ isa_attach_hook(parent, self, iba)
 	struct device *parent, *self;
 	struct isabus_attach_args *iba;
 {
+	extern int isa_has_been_seen;
 
-	/* Nothing to do. */
+	/*
+	 * Notify others that might need to know that the ISA bus
+	 * has now been attached.
+	 */
+	if (isa_has_been_seen)
+		panic("isaattach: ISA bus already seen!");
+	isa_has_been_seen = 1;
 }