diff --git a/tools/tools/tinderbox/tinderbox.1 b/tools/tools/tinderbox/tinderbox.1
index 4b34506be915..b5546cff01ac 100644
--- a/tools/tools/tinderbox/tinderbox.1
+++ b/tools/tools/tinderbox/tinderbox.1
@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 24, 2004
+.Dd March 15, 2004
 .Dt TINDERBOX 1
 .Os
 .Sh NAME
@@ -285,6 +285,12 @@ if a patch was specified.
 .It NOPORTS
 .Va YES
 .El
+.Pp
+Except for
+.Va CFLAGS
+and
+.Va COPTFLAGS ,
+none of these variables may be overridden by command-line arguments.
 .Sh SEE ALSO
 .Xr cvs 1 ,
 .Xr make 1 ,
diff --git a/tools/tools/tinderbox/tinderbox.pl b/tools/tools/tinderbox/tinderbox.pl
index 55f25b7a5c24..24e10a231284 100644
--- a/tools/tools/tinderbox/tinderbox.pl
+++ b/tools/tools/tinderbox/tinderbox.pl
@@ -485,13 +485,11 @@ MAIN:{
 
 	'TARGET'		=> $machine,
 	'TARGET_ARCH'		=> $arch,
-
-	'CFLAGS'		=> "-O -pipe",
     );
 
     # Kernel-specific variables
     if ($cmds{'generic'} || $cmds{'lint'} || $cmds{'release'}) {
-	$ENV{'COPTFLAGS'} = "-O -pipe";
+	# None at the moment
     }
 
     # Release-specific variables
@@ -523,6 +521,18 @@ MAIN:{
 	    $ENV{$key} = $userenv{$key};
 	}
     }
+
+    # Defaults for overridable variables
+    if (!exists($ENV{'CFLAGS'})) {
+	$ENV{'CFLAGS'} = "-O -pipe";
+    }
+    if ($cmds{'generic'} || $cmds{'lint'} || $cmds{'release'}) {
+	if (!exists($ENV{'COPTFLAGS'})) {
+	    $ENV{'COPTFLAGS'} = "-O -pipe";
+	}
+    }
+
+    # List the environment when verbose
     if ($verbose && $verbose > 1) {
 	foreach my $key (sort(keys(%ENV))) {
 	    message("$key=$ENV{$key}\n");