Index: sbin/geom/class/part/gpart.8
===================================================================
--- sbin/geom/class/part/gpart.8
+++ sbin/geom/class/part/gpart.8
@@ -1183,6 +1183,11 @@
 present as independent partition.
 .Em NOTE :
 This may break a mirrored volume and lead to data damage.
+.It Va kern.geom.part.mbr.enforce_chs : No 1
+This variable controls how the Master Boot Record (MBR) module does alignment.
+If this variable set to non zero value, the module will automatically
+recalculate specified by user offset and size to be aligned to the CHS geometry.
+Otherwise the values will be left unchanged.
 .El
 .Sh EXIT STATUS
 Exit status is 0 on success, and 1 if the command fails.
Index: sys/geom/part/g_part_mbr.c
===================================================================
--- sys/geom/part/g_part_mbr.c
+++ sys/geom/part/g_part_mbr.c
@@ -49,6 +49,14 @@
 
 FEATURE(geom_part_mbr, "GEOM partitioning class for MBR support");
 
+SYSCTL_DECL(_kern_geom_part);
+static SYSCTL_NODE(_kern_geom_part, OID_AUTO, mbr, CTLFLAG_RW, 0,
+    "GEOM_PART_MBR Master Boot Record");
+
+static u_int enforce_chs = 1;
+SYSCTL_UINT(_kern_geom_part_mbr, OID_AUTO, enforce_chs,
+    CTLFLAG_RWTUN, &enforce_chs, 1, "Enforce alignment to CHS addressing");
+
 #define	MBRSIZE		512
 
 struct g_part_mbr_table {
@@ -200,6 +208,8 @@
 {
 	uint32_t sectors;
 
+	if (enforce_chs == 0)
+		return (0);
 	sectors = basetable->gpt_sectors;
 	if (*size < sectors)
 		return (EINVAL);