diff --git a/Build.sh b/Build.sh
index ce6c127..c59163b 100644
--- a/Build.sh
+++ b/Build.sh
@@ -1,5 +1,5 @@
 #!/bin/sh
-srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.668 2014/10/03 17:32:07 tg Exp $'
+srcversion='$MirOS: src/bin/mksh/Build.sh,v 1.669 2014/10/07 15:22:12 tg Exp $'
 #-
 # Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
 #		2011, 2012, 2013, 2014
@@ -1784,7 +1784,7 @@ else
 		#define EXTERN
 		#define MKSH_INCLUDES_ONLY
 		#include "sh.h"
-		__RCSID("$MirOS: src/bin/mksh/Build.sh,v 1.668 2014/10/03 17:32:07 tg Exp $");
+		__RCSID("$MirOS: src/bin/mksh/Build.sh,v 1.669 2014/10/07 15:22:12 tg Exp $");
 		int main(void) { printf("Hello, World!\n"); return (isatty(0)); }
 EOF
 	case $cm in
@@ -2316,7 +2316,7 @@ addsrcs '!' HAVE_STRLCPY strlcpy.c
 addsrcs USE_PRINTF_BUILTIN printf.c
 test 1 = "$USE_PRINTF_BUILTIN" && add_cppflags -DMKSH_PRINTF_BUILTIN
 test 1 = "$HAVE_CAN_VERB" && CFLAGS="$CFLAGS -verbose"
-add_cppflags -DMKSH_BUILD_R=503
+add_cppflags -DMKSH_BUILD_R=504
 
 $e $bi$me: Finished configuration testing, now producing output.$ao
 
diff --git a/Makefile b/Makefile
index 1720d7f..e14f564 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-# $MirOS: src/bin/mksh/Makefile,v 1.137 2014/10/03 17:32:08 tg Exp $
+# $MirOS: src/bin/mksh/Makefile,v 1.138 2014/10/07 15:22:13 tg Exp $
 #-
 # Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
 #		2011, 2012, 2013, 2014
@@ -55,7 +55,7 @@ CPPFLAGS+=	-DMKSH_ASSUME_UTF8 -DMKSH_DISABLE_DEPRECATED \
 		-DHAVE_SETGROUPS=1 -DHAVE_STRERROR=0 -DHAVE_STRSIGNAL=0 \
 		-DHAVE_STRLCPY=1 -DHAVE_FLOCK_DECL=1 -DHAVE_REVOKE_DECL=1 \
 		-DHAVE_SYS_ERRLIST_DECL=1 -DHAVE_SYS_SIGLIST_DECL=1 \
-		-DHAVE_PERSISTENT_HISTORY=1 -DMKSH_BUILD_R=503
+		-DHAVE_PERSISTENT_HISTORY=1 -DMKSH_BUILD_R=504
 CPPFLAGS+=	-D${${PROG:L}_tf:C/(Mir${MAN:E}{0,1}){2}/4/:S/x/mksh_BUILD/:U}
 CPPFLAGS+=	-I.
 COPTS+=		-std=c89 -Wall
diff --git a/check.t b/check.t
index 17e104d..2e1d032 100644
--- a/check.t
+++ b/check.t
@@ -1,4 +1,4 @@
-# $MirOS: src/bin/mksh/check.t,v 1.660 2014/10/04 11:47:16 tg Exp $
+# $MirOS: src/bin/mksh/check.t,v 1.661 2014/10/07 15:22:14 tg Exp $
 # OpenBSD src/regress/bin/ksh updated: 2013/12/02 20:39:44
 #-
 # Copyright © 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
@@ -27,7 +27,7 @@
 # http://www.freebsd.org/cgi/cvsweb.cgi/src/tools/regression/bin/test/regress.sh?rev=HEAD
 
 expected-stdout:
-	@(#)MIRBSD KSH R50 2014/10/04
+	@(#)MIRBSD KSH R50 2014/10/07
 description:
 	Check version of shell.
 stdin:
@@ -36,7 +36,7 @@ name: KSH_VERSION
 category: shell:legacy-no
 ---
 expected-stdout:
-	@(#)LEGACY KSH R50 2014/10/04
+	@(#)LEGACY KSH R50 2014/10/07
 description:
 	Check version of legacy shell.
 stdin:
@@ -3736,12 +3736,18 @@ expected-stdout:
 name: IFS-subst-3
 description:
 	Check leading IFS non-whitespace after trim does make a field
+	but leading IFS whitespace does not, nor empty replacements
 stdin:
 	showargs() { for i; do echo -n " <$i>"; done; echo; }
+	showargs 0 ${-+}
 	IFS=:
 	showargs 1 ${-+:foo:bar}
+	IFS=' '
+	showargs 2 ${-+ foo bar}
 expected-stdout:
+	 <0>
 	 <1> <> <foo> <bar>
+	 <2> <foo> <bar>
 ---
 name: IFS-subst-4-1
 description:
diff --git a/eval.c b/eval.c
index 3bf183c..49a4c33 100644
--- a/eval.c
+++ b/eval.c
@@ -23,7 +23,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/eval.c,v 1.152 2014/10/03 17:32:11 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/eval.c,v 1.153 2014/10/07 15:22:16 tg Exp $");
 
 /*
  * string expansion
@@ -62,6 +62,7 @@ typedef struct {
 #define IFS_WORD	0	/* word has chars (or quotes) */
 #define IFS_WS		1	/* have seen IFS white-space */
 #define IFS_NWS		2	/* have seen IFS non-white-space */
+#define IFS_IWS		3	/* begin of word, ignore IFS WS */
 
 static int varsub(Expand *, const char *, const char *, int *, int *);
 static int comsub(Expand *, const char *, int);
@@ -663,7 +664,7 @@ expand(
 						f |= DOTEMP;
 						/* FALLTHROUGH */
 					default:
-						word = IFS_WORD;
+						word = quote ? IFS_WORD : IFS_IWS;
 						/* Enable tilde expansion */
 						tilde_ok = 1;
 						f |= DOTILDE;
@@ -907,12 +908,12 @@ expand(
 			 *	IFS_WORD		w/WS	w/NWS	w
 			 *	IFS_WS			-/WS	-/NWS	-
 			 *	IFS_NWS			-/NWS	w/NWS	-
+			 *	IFS_IWS			-/WS	w/NWS	-
 			 * (w means generate a word)
-			 * Note that IFS_NWS/0 generates a word (AT&T ksh
-			 * doesn't do this, but POSIX does).
 			 */
-			if (word == IFS_WORD ||
-			    (word == IFS_NWS && c && !ctype(c, C_IFSWS))) {
+			if ((word == IFS_WORD) || (c &&
+			    (word == IFS_IWS || word == IFS_NWS) &&
+			    !ctype(c, C_IFSWS))) {
  emit_word:
 				*dp++ = '\0';
 				cp = Xclose(ds, dp);
diff --git a/sh.h b/sh.h
index 6e68e9f..b3d1c0b 100644
--- a/sh.h
+++ b/sh.h
@@ -169,9 +169,9 @@
 #endif
 
 #ifdef EXTERN
-__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.696 2014/10/04 11:47:18 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.697 2014/10/07 15:22:17 tg Exp $");
 #endif
-#define MKSH_VERSION "R50 2014/10/04"
+#define MKSH_VERSION "R50 2014/10/07"
 
 /* arithmetic types: C implementation */
 #if !HAVE_CAN_INTTYPES
@@ -533,7 +533,7 @@ char *ucstrstr(char *, const char *);
 #define mkssert(e)	do { } while (/* CONSTCOND */ 0)
 #endif
 
-#if (!defined(MKSH_BUILDMAKEFILE4BSD) && !defined(MKSH_BUILDSH)) || (MKSH_BUILD_R != 503)
+#if (!defined(MKSH_BUILDMAKEFILE4BSD) && !defined(MKSH_BUILDSH)) || (MKSH_BUILD_R != 504)
 #error Must run Build.sh to compile this.
 extern void thiswillneverbedefinedIhope(void);
 int