diff --git a/sys/i386/isa/diskslice_machdep.c b/sys/i386/isa/diskslice_machdep.c
index 313b03cb8fa5..ed6fd7065050 100644
--- a/sys/i386/isa/diskslice_machdep.c
+++ b/sys/i386/isa/diskslice_machdep.c
@@ -35,7 +35,7 @@
  *
  *	from: @(#)ufs_disksubr.c	7.16 (Berkeley) 5/4/91
  *	from: ufs_disksubr.c,v 1.8 1994/06/07 01:21:39 phk Exp $
- *	$Id: diskslice_machdep.c,v 1.10 1995/04/20 01:21:51 phk Exp $
+ *	$Id: diskslice_machdep.c,v 1.11 1995/04/20 06:01:51 phk Exp $
  */
 
 #include <stddef.h>
@@ -104,7 +104,9 @@ check_part(sname, dp, offset, nsectors, ntracks, mbr_offset )
 	if (ssector < ssector1
 	    && ((chs_ssect == nsectors && dp->dp_shd == ntracks - 1
 		 && chs_scyl == 1023)
-		|| (ssector1 - ssector) % (1024 * secpercyl) == 0)) {
+		|| (ssector1 - ssector) % (1024 * secpercyl) == 0)
+		|| (dp->dp_ssect == 255 && dp->dp_shd == 255 && 
+		dp->dp_scyl == 255)) {
 		TRACE(("%s: C/H/S start %d/%d/%d, start %lu: allow\n",
 		       sname, chs_scyl, dp->dp_shd, chs_ssect, ssector1));
 		ssector = ssector1;
@@ -120,7 +122,9 @@ check_part(sname, dp, offset, nsectors, ntracks, mbr_offset )
 	if (esector < esector1
 	    && ((chs_esect == nsectors && dp->dp_ehd == ntracks - 1
 		 && chs_ecyl == 1023)
-		|| (esector1 - esector) % (1024 * secpercyl) == 0)) {
+		|| (esector1 - esector) % (1024 * secpercyl) == 0)
+		|| (dp->dp_esect == 255 && dp->dp_ehd == 255 && 
+		dp->dp_ecyl == 255)) {
 		TRACE(("%s: C/H/S end %d/%d/%d, end %lu: allow\n",
 		       sname, chs_ecyl, dp->dp_ehd, chs_esect, esector1));
 		esector = esector1;
diff --git a/sys/kern/subr_diskmbr.c b/sys/kern/subr_diskmbr.c
index 313b03cb8fa5..ed6fd7065050 100644
--- a/sys/kern/subr_diskmbr.c
+++ b/sys/kern/subr_diskmbr.c
@@ -35,7 +35,7 @@
  *
  *	from: @(#)ufs_disksubr.c	7.16 (Berkeley) 5/4/91
  *	from: ufs_disksubr.c,v 1.8 1994/06/07 01:21:39 phk Exp $
- *	$Id: diskslice_machdep.c,v 1.10 1995/04/20 01:21:51 phk Exp $
+ *	$Id: diskslice_machdep.c,v 1.11 1995/04/20 06:01:51 phk Exp $
  */
 
 #include <stddef.h>
@@ -104,7 +104,9 @@ check_part(sname, dp, offset, nsectors, ntracks, mbr_offset )
 	if (ssector < ssector1
 	    && ((chs_ssect == nsectors && dp->dp_shd == ntracks - 1
 		 && chs_scyl == 1023)
-		|| (ssector1 - ssector) % (1024 * secpercyl) == 0)) {
+		|| (ssector1 - ssector) % (1024 * secpercyl) == 0)
+		|| (dp->dp_ssect == 255 && dp->dp_shd == 255 && 
+		dp->dp_scyl == 255)) {
 		TRACE(("%s: C/H/S start %d/%d/%d, start %lu: allow\n",
 		       sname, chs_scyl, dp->dp_shd, chs_ssect, ssector1));
 		ssector = ssector1;
@@ -120,7 +122,9 @@ check_part(sname, dp, offset, nsectors, ntracks, mbr_offset )
 	if (esector < esector1
 	    && ((chs_esect == nsectors && dp->dp_ehd == ntracks - 1
 		 && chs_ecyl == 1023)
-		|| (esector1 - esector) % (1024 * secpercyl) == 0)) {
+		|| (esector1 - esector) % (1024 * secpercyl) == 0)
+		|| (dp->dp_esect == 255 && dp->dp_ehd == 255 && 
+		dp->dp_ecyl == 255)) {
 		TRACE(("%s: C/H/S end %d/%d/%d, end %lu: allow\n",
 		       sname, chs_ecyl, dp->dp_ehd, chs_esect, esector1));
 		esector = esector1;