diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index 930b1d14b72e..df27d850be18 100644
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: machdep.c,v 1.191 1996/03/01 21:49:49 scottr Exp $	*/
+/*	$NetBSD: machdep.c,v 1.192 1996/03/05 01:28:51 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1993, 1994, 1995 Charles M. Hannum.  All rights reserved.
@@ -1102,11 +1102,19 @@ init386(first_avail)
 	/*
 	 * Use BIOS values stored in RTC CMOS RAM, since probing
 	 * breaks certain 386 AT relics.
+	 *
+	 * XXX Not only does probing break certain 386 AT relics, but
+	 * not all BIOSes (Dell, Compaq, others) report the correct
+	 * amount of extended memory.
 	 */
 	biosbasemem = (mc146818_read(NULL, NVRAM_BASEHI) << 8) |
 	    mc146818_read(NULL, NVRAM_BASELO);
+#ifdef EXTMEM_SIZE
+	biosextmem = EXTMEM_SIZE;
+#else
 	biosextmem = (mc146818_read(NULL, NVRAM_EXTHI) << 8) |
 	    mc146818_read(NULL, NVRAM_EXTLO);
+#endif /* EXTMEM_SIZE */
 
 	/* Round down to whole pages. */
 	biosbasemem &= -(NBPG / 1024);