diff --git a/bin/autom4te.in b/bin/autom4te.in
index 798013a..e5443e3 100644
--- a/bin/autom4te.in
+++ b/bin/autom4te.in
@@ -83,6 +83,10 @@ my @preselect = ('include',
 # M4 include path.
 my @include;
 
+# M4 define/undefine.
+my @define;
+my @undefine;
+
 # Do we freeze?
 my $freeze = 0;
 
@@ -176,6 +180,10 @@ Library directories:
   -B, --prepend-include=DIR  prepend directory DIR to search path
   -I, --include=DIR          append directory DIR to search path
 
+m4 arguments:
+  -D, --define=NAME[=VALUE]  define NAME as having VALUE, or empty
+  -U, --undefine=NAME        undefine NAME
+
 Tracing:
   -t, --trace=MACRO[:FORMAT]  report the MACRO invocations
   -p, --preselect=MACRO       prepare to trace MACRO in a future run
@@ -345,6 +353,8 @@ sub parse_args ()
      # Library directories:
      "B|prepend-include=s" => address@hidden,
      "I|include=s"         => address@hidden,
+     "D|define=s"          => address@hidden,
+     "U|undefine=s"        => address@hidden,
 
      # Tracing:
      # Using a hash for traces is seducing.  Unfortunately, upon '-t FOO',
@@ -465,6 +475,8 @@ sub handle_m4 ($@)
   xsystem ("$m4 @M4_GNU@"
 	   . join (' --include=', '', map { shell_quote ($_) } @include)
 	   . ' --debug=aflq'
+	   . join (' --define=', '', map { shell_quote ($_) } @define)
+	   . join (' --undefine=', '', map { shell_quote ($_) } @undefine)
 	   . (!exists $ENV{'AUTOM4TE_NO_FATAL'} ? ' --fatal-warning' : '')
 	   . " @address@hidden" . shell_quote ("$tcache" . $req->id . "t")
 	   . join (' --trace=', '', map { shell_quote ($_) } sort @macro)