diff --git a/bin/sh/eval.c b/bin/sh/eval.c
index 585f91ead32a..92a18e4b2b3b 100644
--- a/bin/sh/eval.c
+++ b/bin/sh/eval.c
@@ -745,8 +745,9 @@ evalcommand(union node *cmd, int flags, struct backcmd *backcmd)
 	/* Print the command if xflag is set. */
 	if (xflag) {
 		char sep = 0;
-		const char *p;
-		out2str(ps4val());
+		const char *p, *ps4;
+		ps4 = expandstr(ps4val());
+		out2str(ps4 != NULL ? ps4 : ps4val());
 		for (sp = varlist.list ; sp ; sp = sp->next) {
 			if (sep != 0)
 				out2c(' ');
diff --git a/bin/sh/expand.c b/bin/sh/expand.c
index 108a77c4be68..aaa91acc3392 100644
--- a/bin/sh/expand.c
+++ b/bin/sh/expand.c
@@ -174,6 +174,7 @@ expandarg(union node *arg, struct arglist *arglist, int flag)
 	ifslastp = NULL;
 	argstr(arg->narg.text, flag);
 	if (arglist == NULL) {
+		STACKSTRNUL(expdest);
 		return;			/* here document expanded */
 	}
 	STPUTC('\0', expdest);
diff --git a/bin/sh/parser.c b/bin/sh/parser.c
index 151970b79d08..2fea1ecb5270 100644
--- a/bin/sh/parser.c
+++ b/bin/sh/parser.c
@@ -2029,3 +2029,47 @@ getprompt(void *unused __unused)
 	ps[i] = '\0';
 	return (ps);
 }
+
+
+const char *
+expandstr(char *ps)
+{
+	union node n;
+	struct jmploc jmploc;
+	struct jmploc *const savehandler = handler;
+	const int saveprompt = doprompt;
+	struct parsefile *const savetopfile = getcurrentfile();
+	struct parser_temp *const saveparser_temp = parser_temp;
+	const char *result = NULL;
+
+	if (!setjmp(jmploc.loc)) {
+		handler = &jmploc;
+		parser_temp = NULL;
+		setinputstring(ps, 1);
+		doprompt = 0;
+		readtoken1(pgetc(), DQSYNTAX, "\n\n", 0);
+		if (backquotelist != NULL)
+			error("Command substitution not allowed here");
+
+		n.narg.type = NARG;
+		n.narg.next = NULL;
+		n.narg.text = wordtext;
+		n.narg.backquote = backquotelist;
+
+		expandarg(&n, NULL, 0);
+		result = stackblock();
+		INTOFF;
+	}
+	handler = savehandler;
+	doprompt = saveprompt;
+	popfilesupto(savetopfile);
+	if (parser_temp != saveparser_temp) {
+		parser_temp_free_all();
+		parser_temp = saveparser_temp;
+	}
+	if (result != NULL) {
+		INTON;
+	} else if (exception == EXINT)
+		raise(SIGINT);
+	return result;
+}
diff --git a/bin/sh/parser.h b/bin/sh/parser.h
index e213e2140617..9a996d04a603 100644
--- a/bin/sh/parser.h
+++ b/bin/sh/parser.h
@@ -82,3 +82,4 @@ void fixredir(union node *, const char *, int);
 int goodname(const char *);
 int isassignment(const char *);
 char *getprompt(void *);
+const char *expandstr(char *);
diff --git a/bin/sh/sh.1 b/bin/sh/sh.1
index 42e55d391b3e..0ce07bd9f0ce 100644
--- a/bin/sh/sh.1
+++ b/bin/sh/sh.1
@@ -32,7 +32,7 @@
 .\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
 .\" $FreeBSD$
 .\"
-.Dd May 21, 2011
+.Dd June 9, 2011
 .Dt SH 1
 .Os
 .Sh NAME
@@ -324,7 +324,7 @@ Useful for debugging.
 Write each command
 (preceded by the value of the
 .Va PS4
-variable)
+variable subjected to parameter expansion and arithmetic expansion)
 to standard error before it is executed.
 Useful for debugging.
 .El
diff --git a/tools/regression/bin/sh/execution/set-x3.0 b/tools/regression/bin/sh/execution/set-x3.0
new file mode 100644
index 000000000000..1ca57aca6baa
--- /dev/null
+++ b/tools/regression/bin/sh/execution/set-x3.0
@@ -0,0 +1,9 @@
+# $FreeBSD$
+
+key='must contain this'
+PS4='$key+ '
+{ r=`set -x; { :; } 2>&1 >/dev/null`; } 2>/dev/null
+case $r in
+*"$key"*) true ;;
+*) false ;;
+esac