diff --git a/usr.bin/m4/extern.h b/usr.bin/m4/extern.h
index 1cb9de13da9e..5c73798bd6f6 100644
--- a/usr.bin/m4/extern.h
+++ b/usr.bin/m4/extern.h
@@ -1,5 +1,5 @@
 /*	$OpenBSD: extern.h,v 1.49 2009/10/14 17:19:47 sthen Exp $	*/
-/*	$NetBSD: extern.h,v 1.19 2016/01/16 18:30:57 christos Exp $	*/
+/*	$NetBSD: extern.h,v 1.19.18.1 2020/07/07 10:40:46 martin Exp $	*/
 
 /*-
  * Copyright (c) 1991, 1993
@@ -146,7 +146,7 @@ extern char *endest;
 /* trace.c */
 extern unsigned int trace_flags;
 #define TRACE_ALL	512
-extern void trace_file(const char *);
+extern int trace_file(const char *);
 extern size_t trace(const char **, int, struct input_file *);
 extern void finish_trace(size_t);
 extern void set_trace_flags(const char *);
diff --git a/usr.bin/m4/m4.1 b/usr.bin/m4/m4.1
index f033cee72bbb..ae0c2cbc4f39 100644
--- a/usr.bin/m4/m4.1
+++ b/usr.bin/m4/m4.1
@@ -1,4 +1,4 @@
-.\"	$NetBSD: m4.1,v 1.27 2016/01/17 11:24:28 wiz Exp $
+.\"	$NetBSD: m4.1,v 1.27.18.1 2020/07/07 10:40:46 martin Exp $
 .\"	@(#) $OpenBSD: m4.1,v 1.56 2009/10/14 17:19:47 sthen Exp $
 .\"
 .\" Copyright (c) 1989, 1993
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd January 16, 2015
+.Dd June 25, 2020
 .Dt M4 1
 .Os
 .Sh NAME
@@ -46,7 +46,6 @@
 .Sm on
 .Oc
 .Op Fl d Ar flags
-.Op Fl e Ar filename
 .Op Fl F Ar filename
 .Op Fl I Ar dirname
 .Op Fl L Ar number
@@ -138,8 +137,6 @@ By default, trace is set to
 Warnings make
 .Nm
 exit.
-.It Fl e , Fl Fl error-output Ar filename
-Redirect error output to filename.
 .It Fl F , Fl Fl freeze-state Ar filename
 Save the input state to
 .Ar filename .
@@ -166,7 +163,7 @@ Set unbuffered output, disable tty signals.
 .It Fl L , Fl Fl nesting-limit
 Set the nesting limit in macro expansions.
 This is unimplemented and unlimited.
-.It Fl o Ar filename
+.It Fl o , Fl Fl error-output Ar filename
 Send trace output to
 .Ar filename .
 .It Fl P , Fl Fl prefix-builtins
diff --git a/usr.bin/m4/main.c b/usr.bin/m4/main.c
index 2a38bb36686c..453c2d3598b5 100644
--- a/usr.bin/m4/main.c
+++ b/usr.bin/m4/main.c
@@ -1,5 +1,5 @@
 /*	$OpenBSD: main.c,v 1.77 2009/10/14 17:19:47 sthen Exp $	*/
-/*	$NetBSD: main.c,v 1.48 2019/03/26 16:41:06 christos Exp $	*/
+/*	$NetBSD: main.c,v 1.48.2.1 2020/07/07 10:40:46 martin Exp $	*/
 
 /*-
  * Copyright (c) 1989, 1993
@@ -42,7 +42,7 @@
 #include "nbtool_config.h"
 #endif
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: main.c,v 1.48 2019/03/26 16:41:06 christos Exp $");
+__RCSID("$NetBSD: main.c,v 1.48.2.1 2020/07/07 10:40:46 martin Exp $");
 #include <assert.h>
 #include <signal.h>
 #include <getopt.h>
@@ -196,7 +196,7 @@ onintr(int signo)
 struct option longopts[] = {
 	{ "debug",		optional_argument,	0, 'd' },
 	{ "define",		required_argument,	0, 'D' },
-	{ "error-output",	required_argument,	0, 'e' },
+	{ "error-output",	required_argument,	0, 'o' }, /* sic */
 	{ "fatal-warnings",	no_argument,		0, 'E' },
 	{ "freeze-state",	required_argument,	0, 'F' },
 	{ "gnu",		no_argument,		0, 'g' },
@@ -227,8 +227,8 @@ main(int argc, char *argv[])
 {
 	int c;
 	int n;
+	int error;
 	char *p;
-	FILE *sfp;
 
 	setprogname(argv[0]);
 
@@ -246,7 +246,7 @@ main(int argc, char *argv[])
 	outfile = NULL;
 	resizedivs(MAXOUT);
 
-	while ((c = getopt_long(argc, argv, "D:d:e:EF:GgI:iL:o:PR:Qst:U:v",
+	while ((c = getopt_long(argc, argv, "D:d:EF:GgI:iL:o:PR:Qst:U:v",
 	    longopts, NULL)) != -1)
 		switch(c) {
 		case 'D':               /* define something..*/
@@ -263,18 +263,6 @@ main(int argc, char *argv[])
 		case 'E':
 			fatal_warnings++;
 			break;
-		case 'e':
-			/*
-			 * Don't use freopen here because if it fails
-			 * we lose stderr, instead trash it.
-			 */
-			if ((sfp = fopen(optarg, "w+")) == NULL) {
-				warn("Can't redirect errors to `%s'", optarg);
-				break;
-			}
-			fclose(stderr);
-			memcpy(stderr, sfp, sizeof(*sfp));
-			break;
 		case 'F':
 			freeze = optarg;
 #ifndef REAL_FREEZE
@@ -299,7 +287,9 @@ main(int argc, char *argv[])
 			nesting_limit = atoi(optarg);
 			break;
 		case 'o':
-			trace_file(optarg);
+			error = trace_file(optarg);
+			if (error)
+				warn("%s", optarg);
                         break;
 		case 'P':
 			prefix_builtins = 1;
diff --git a/usr.bin/m4/trace.c b/usr.bin/m4/trace.c
index bb9397fedfee..4d5d48ec4e4c 100644
--- a/usr.bin/m4/trace.c
+++ b/usr.bin/m4/trace.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: trace.c,v 1.8 2012/03/20 20:34:58 matt Exp $	*/
+/*	$NetBSD: trace.c,v 1.8.34.1 2020/07/07 10:40:46 martin Exp $	*/
 /* $OpenBSD: trace.c,v 1.15 2006/03/24 08:03:44 espie Exp $ */
 /*
  * Copyright (c) 2001 Marc Espie.
@@ -28,7 +28,7 @@
 #include "nbtool_config.h"
 #endif
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: trace.c,v 1.8 2012/03/20 20:34:58 matt Exp $");
+__RCSID("$NetBSD: trace.c,v 1.8.34.1 2020/07/07 10:40:46 martin Exp $");
 
 #include <sys/types.h>
 #include <err.h>
@@ -59,15 +59,27 @@ static int frame_level(void);
 
 unsigned int trace_flags = TRACE_QUOTE | TRACE_EXPANSION;
 
-void
+int
 trace_file(const char *name)
 {
+	FILE *newfp;
+
+	if (name == NULL)
+		newfp = stderr;
+#if 0 /* not yet */
+	else if (*name == '\0')
+		newfp = NULL;
+#endif
+	else {
+		newfp = fopen(name, "a");
+		if (newfp == NULL)
+			return -1;
+	}
 
 	if (traceout && traceout != stderr)
 		fclose(traceout);
-	traceout = fopen(name, "w");
-	if (!traceout)
-		err(1, "can't open %s", name);
+	traceout = newfp;
+	return 0;
 }
 
 static unsigned int