diff --git a/misc.c b/misc.c
index c9edb5e..fe9d309 100644
--- a/misc.c
+++ b/misc.c
@@ -32,7 +32,7 @@
 #include <grp.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.277 2017/05/05 22:53:30 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.278 2017/08/07 20:49:41 tg Exp $");
 
 #define KSH_CHVT_FLAG
 #ifdef MKSH_SMALL
@@ -271,6 +271,11 @@ change_flag(enum sh_flag f, int what, bool newset)
 	} else if ((f == FPOSIX || f == FSH) && newval) {
 		/* Turning on -o posix or -o sh? */
 		Flag(FBRACEEXPAND) = 0;
+		/* Turning on -o posix? */
+		if (f == POSIX) {
+			/* C locale required for compliance */
+			UTFMODE = 0;
+		}
 	} else if (f == FTALKING) {
 		/* Changing interactive flag? */
 		if ((what == OF_CMDLINE || what == OF_SET) && procpid == kshpid)
diff --git a/mksh.1 b/mksh.1
index e295d9c..4ae26e6 100644
--- a/mksh.1
+++ b/mksh.1
@@ -1,4 +1,4 @@
-.\" $MirOS: src/bin/mksh/mksh.1,v 1.447 2017/05/05 22:45:57 tg Exp $
+.\" $MirOS: src/bin/mksh/mksh.1,v 1.448 2017/08/07 20:49:42 tg Exp $
 .\" $OpenBSD: ksh.1,v 1.160 2015/07/04 13:27:04 feinerer Exp $
 .\"-
 .\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
@@ -76,7 +76,7 @@
 .\" with -mandoc, it might implement .Mx itself, but we want to
 .\" use our own definition. And .Dd must come *first*, always.
 .\"
-.Dd $Mdocdate: May 5 2017 $
+.Dd $Mdocdate: August 7 2017 $
 .\"
 .\" Check which macro package we use, and do other -mdoc setup.
 .\"
@@ -4308,9 +4308,11 @@ Automatically enabled if the basename of the shell invocation begins with
 .Dq sh
 and this autodetection feature is compiled in
 .Pq not in MirBSD .
-As a side effect, setting this flag turns off
+As a side effect, setting this flag turns off the
 .Ic braceexpand
-mode, which can be turned back on manually, and
+and
+.Ic utf8\-mode
+flags, which can be turned back on manually, and
 .Ic sh
 mode (unless both are enabled at the same time).
 .It Fl o Ic sh
@@ -6640,12 +6642,14 @@ supports only the
 locale.
 .Nm mksh Ns 's
 .Ic utf8\-mode
+.Em must
+be disabled in POSIX mode, and it
 only supports the Unicode BMP (Basic Multilingual Plane) and maps
 raw octets into the U+EF80..U+EFFF wide character range; compare
 .Sx Arithmetic expressions .
 The following
 .Tn POSIX
-.Nm sh
+.Nm sh Ns -compatible
 code toggles the
 .Ic utf8\-mode
 option dependent on the current