diff --git a/Build.sh b/Build.sh
index 98673e5..a75abd2 100644
--- a/Build.sh
+++ b/Build.sh
@@ -1,5 +1,5 @@
 #!/bin/sh
-srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.516 2012/03/27 21:01:55 tg Exp $'
+srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.517 2012/03/27 21:23:50 tg Exp $'
 #-
 # Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
 #		2011, 2012
@@ -1335,7 +1335,7 @@ else
 		#define EXTERN
 		#define MKSH_INCLUDES_ONLY
 		#include "sh.h"
-		__RCSID("$MirOS: src/bin/mksh/Build.sh,v 1.516 2012/03/27 21:01:55 tg Exp $");
+		__RCSID("$MirOS: src/bin/mksh/Build.sh,v 1.517 2012/03/27 21:23:50 tg Exp $");
 		int main(void) { printf("Hello, World!\n"); return (0); }
 EOF
 	case $cm in
@@ -1752,6 +1752,7 @@ addsrcs '!' HAVE_STRLCPY strlcpy.c
 addsrcs USE_PRINTF_BUILTIN printf.c
 test 1 = "$USE_PRINTF_BUILTIN" && add_cppflags -DMKSH_PRINTF_BUILTIN
 test 1 = "$HAVE_CAN_VERB" && CFLAGS="$CFLAGS -verbose"
+add_cppflags -DMKSH_BUILDSH
 
 $e $bi$me: Finished configuration testing, now producing output.$ao
 
diff --git a/Makefile b/Makefile
index 8a54669..78c4d7c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-# $MirOS: src/bin/mksh/Makefile,v 1.93 2012/03/23 19:38:11 tg Exp $
+# $MirOS: src/bin/mksh/Makefile,v 1.94 2012/03/27 21:23:51 tg Exp $
 #-
 # Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
 #	Thorsten Glaser <tg@mirbsd.org>
@@ -48,6 +48,7 @@ CPPFLAGS+=	-DMKSH_ASSUME_UTF8 -DMKSH_DISABLE_DEPRECATED \
 		-DHAVE_PERSISTENT_HISTORY=1
 # probably differs between i386 and sparc
 CPPFLAGS+=	-DHAVE_SILENT_IDIVWRAPV=0
+CPPFLAGS+=	-D${${PROG:L}_tf:C/(Mir${MAN:E}{0,1}){2}/4/:S/x/mksh_BUILD/:U}
 COPTS+=		-std=gnu99 -Wall
 .endif
 
@@ -95,6 +96,7 @@ cleandir: clean-extra
 clean-extra: .PHONY
 	-rm -rf build-dir regress-dir printf.o printf.ln
 
+mksh_tf=xMakefile${OStype:S/${MACHINE_OS}/1/1g}${OSNAME}
 distribution:
 	sed 's!\$$I''d\([:$$]\)!$$M''irSecuCron\1!g' \
 	    ${.CURDIR}/dot.mkshrc >${DESTDIR}/etc/skel/.mkshrc
diff --git a/sh.h b/sh.h
index 1bfca86..8e517c9 100644
--- a/sh.h
+++ b/sh.h
@@ -152,7 +152,7 @@
 #endif
 
 #ifdef EXTERN
-__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.529 2012/03/26 21:10:44 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.530 2012/03/27 21:23:52 tg Exp $");
 #endif
 #define MKSH_VERSION "R40 2012/03/26"
 
@@ -429,6 +429,11 @@ char *ucstrstr(char *, const char *);
 #define mkssert(e)	((void)0)
 #endif
 
+#if !defined(MKSH_BUILDMAKEFILE4BSD) && !defined(MKSH_BUILDSH)
+I'm sorry, Dave. I'm afraid I can't do that.
+#error Must run Build.sh to compile this.
+#endif
+
 /* use this ipv strchr(s, 0) but no side effects in s! */
 #define strnul(s)	((s) + strlen(s))