diff --git a/usr.bin/m4/m4.1 b/usr.bin/m4/m4.1
--- a/usr.bin/m4/m4.1
+++ b/usr.bin/m4/m4.1
@@ -33,7 +33,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 8, 2021
+.Dd June 21, 2023
 .Dt M4 1
 .Os
 .Sh NAME
@@ -47,7 +47,7 @@
 .Fl D Ar name Op No = Ar value
 .Sm on
 .Oc
-.Op Fl d Ar flags
+.Op Fl d Oo Oo +- Oc Ns Ar flags Oc
 .Op Fl I Ar dirname
 .Op Fl o Ar filename
 .Op Fl t Ar macro
@@ -98,15 +98,14 @@
 .Pp
 The options are as follows:
 .Bl -tag -width Ds
-.It Fl D Ns Ar name Ns Op = Ns Ar value
+.It Fl D Ns Ar name Ns Oo = Ns Ar value Oc , Fl -define Ns = Ns Ar name Ns Oo = Ns Ar value Oc
 Define the symbol
 .Ar name
 to have some value (or
 .Dv NULL ) .
-.It Fl d Ar "flags"
-Set trace flags.
-.Ar flags
-may hold the following:
+.It Fl d Oo Oo +|- Oc Ns Ar flags Oc , Fl -debug Ns = Ns Oo Oo +|- Oc Ns Ar flags Oc
+Set or unset trace flags.
+The trace flags are as follows:
 .Bl -tag -width Ds
 .It Ar a
 print macro arguments.
@@ -128,9 +127,21 @@
 turn on all options.
 .El
 .Pp
+If
+.Qq +
+or
+.Qq -
+is used, the specified flags are added to or removed from the set of
+active trace flags, respectively; otherwise, the specified flags
+replace the set of active trace flags.
+.Pp
+Specifying this option without an argument is equivalent to specifying
+it with the argument
+.Qq aeq .
+.Pp
 By default, trace is set to
 .Qq eq .
-.It Fl E
+.It Fl E , Fl -fatal-warnings
 Set warnings to be fatal.
 When a single
 .Fl E
@@ -145,7 +156,7 @@
 .Nm
 will exit with a non-zero exit status.
 This behaviour matches GNU-m4 1.4.9 and later.
-.It Fl g
+.It Fl g , Fl -gnu
 Activate GNU-m4 compatibility mode.
 In this mode, translit handles simple character
 ranges (e.g., a-z), regular expressions mimic emacs behavior,
@@ -155,27 +166,27 @@
 and eval understands
 .Sq 0rbase:value
 numbers.
-.It Fl I Ar "dirname"
+.It Fl I Ar dirname , Fl -include Ns = Ns Ar dirname
 Add directory
 .Ar dirname
 to the include path.
-.It Fl o Ar filename
+.It Fl o Ar filename , Fl -error-output Ns = Ns Ar filename
 Send trace output to
 .Ar filename .
-.It Fl P
+.It Fl P , Fl -prefix-builtins
 Prefix all built-in macros with
 .Sq m4_ .
 For example, instead of writing
 .Ic define ,
 use
 .Ic m4_define .
-.It Fl s
+.It Fl s , Fl -synclines
 Output line synchronization directives, suitable for
 .Xr cpp 1 .
-.It Fl t Ar macro
+.It Fl t Ar macro , Fl -trace Ns = Ns Ar macro
 Turn tracing on for
 .Ar macro .
-.It Fl "U" Ns Ar "name"
+.It Fl U Ns Ar name , Fl -undefine Ns = Ns Ar name
 Undefine the symbol
 .Ar name .
 .El
diff --git a/usr.bin/m4/main.c b/usr.bin/m4/main.c
--- a/usr.bin/m4/main.c
+++ b/usr.bin/m4/main.c
@@ -47,6 +47,7 @@
 #include <signal.h>
 #include <err.h>
 #include <errno.h>
+#include <getopt.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <ctype.h>
@@ -60,6 +61,21 @@
 #include "extern.h"
 #include "pathnames.h"
 
+static const char *shortopts = "+D:d::EgI:o:Pst:U:";
+static const struct option longopts[] = {
+	{ "define",		required_argument,	NULL,	'D' },
+	{ "debug",		optional_argument,	NULL,	'd' },
+	{ "fatal-warnings",	no_argument,		NULL,	'E' },
+	{ "gnu",		no_argument,		NULL,	'g' },
+	{ "include",		required_argument,	NULL,	'I' },
+	{ "error-output",	required_argument,	NULL,	'o' },
+	{ "prefix-builtins",	no_argument,		NULL,	'P' },
+	{ "synclines",		no_argument,		NULL,	's' },
+	{ "trace",		required_argument,	NULL,	't' },
+	{ "undefine",		required_argument,	NULL,	'U' },
+	{ NULL, 0, NULL, 0 },
+};
+
 stae *mstack;			/* stack of m4 machine         */
 char *sstack;			/* shadow stack, for string space extension */
 static size_t STACKMAX;		/* current maximum size of stack */
@@ -188,7 +204,7 @@
 	outfile = NULL;
 	resizedivs(MAXOUT);
 
-	while ((c = getopt(argc, argv, "gst:d:D:EU:o:I:P")) != -1)
+	while ((c = getopt_long(argc, argv, shortopts, longopts, NULL)) != -1)
 		switch(c) {
 
 		case 'D':               /* define something..*/
@@ -218,7 +234,7 @@
 			mimic_gnu = 1;
 			break;
 		case 'd':
-			set_trace_flags(optarg);
+			set_trace_flags(optarg ? optarg : "aeq");
 			break;
 		case 's':
 			synch_lines = 1;