diff --git a/sbin/mdconfig/mdconfig.8 b/sbin/mdconfig/mdconfig.8
index 6df97aae1ac3..7e722752cfb1 100644
--- a/sbin/mdconfig/mdconfig.8
+++ b/sbin/mdconfig/mdconfig.8
@@ -114,11 +114,11 @@ md prefix.
 Size of the memory disk.
 .Ar Size
 is the number of 512 byte sectors unless suffixed with a
-.Cm k , m , g ,
+.Cm b , k , m , g ,
 or
 .Cm t
 which
-denotes kilobyte, megabyte, gigabyte and terabyte respectively.
+denotes byte, kilobyte, megabyte, gigabyte and terabyte respectively.
 .It Fl S Ar sectorsize
 Sectorsize to use for malloc backed device.
 .It Fl x Ar sectors/track
diff --git a/sbin/mdconfig/mdconfig.c b/sbin/mdconfig/mdconfig.c
index 0e6d81804e20..b2d92667427e 100644
--- a/sbin/mdconfig/mdconfig.c
+++ b/sbin/mdconfig/mdconfig.c
@@ -178,6 +178,8 @@ main(int argc, char **argv)
 			mdio.md_mediasize = (off_t)strtoumax(optarg, &p, 0);
 			if (p == NULL || *p == '\0')
 				mdio.md_mediasize *= DEV_BSIZE;
+			else if (*p == 'b' || *p == 'B')
+				; /* do nothing */
 			else if (*p == 'k' || *p == 'K')
 				mdio.md_mediasize <<= 10;
 			else if (*p == 'm' || *p == 'M')