diff --git a/unix/mkall.sh b/unix/mkall.sh
index d00ab2ff..da57b811 100755
--- a/unix/mkall.sh
+++ b/unix/mkall.sh
@@ -257,5 +257,5 @@ esac
 	esac
 	if [ -n "$mksysctl" ]; then echo "$mksysctl |gofmt >$zsysctl"; fi
 	if [ -n "$mksysnum" ]; then echo "$mksysnum |gofmt >zsysnum_$GOOSARCH.go"; fi
-	if [ -n "$mktypes" ]; then echo "$mktypes types_$GOOS.go |gofmt >ztypes_$GOOSARCH.go"; fi
+	if [ -n "$mktypes" ]; then echo "$mktypes types_$GOOS.go | sed -e '/^package /i\/\/ +build $GOARCH,$GOOS\n' | gofmt >ztypes_$GOOSARCH.go"; fi
 ) | $run
diff --git a/unix/mkerrors.sh b/unix/mkerrors.sh
index 48c62d5c..8e967035 100755
--- a/unix/mkerrors.sh
+++ b/unix/mkerrors.sh
@@ -11,6 +11,11 @@ unset LANG
 export LC_ALL=C
 export LC_CTYPE=C
 
+if test -z "$GOARCH" -o -z "$GOOS"; then
+  echo 1>&2 "GOARCH or GOOS not defined in environment"
+  exit 1
+fi
+
 CC=${CC:-gcc}
 
 uname=$(uname)
@@ -347,6 +352,8 @@ echo '#include <signal.h>' | $CC -x c - -E -dM $ccflags |
 echo '// mkerrors.sh' "$@"
 echo '// MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT'
 echo
+echo "// +build ${GOARCH},${GOOS}"
+echo
 go tool cgo -godefs -- "$@" _const.go >_error.out
 cat _error.out | grep -vf _error.grep | grep -vf _signal.grep
 echo
diff --git a/unix/mksyscall.pl b/unix/mksyscall.pl
index ec0103ca..b1e7766d 100755
--- a/unix/mksyscall.pl
+++ b/unix/mksyscall.pl
@@ -63,6 +63,11 @@ if($ARGV[0] =~ /^-/) {
 	exit 1;
 }
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 sub parseparamlist($) {
 	my ($list) = @_;
 	$list =~ s/^\s*//;
@@ -302,6 +307,8 @@ print <<EOF;
 // $cmdline
 // MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 import (
diff --git a/unix/mksyscall_solaris.pl b/unix/mksyscall_solaris.pl
index e8ec976f..e81edb95 100755
--- a/unix/mksyscall_solaris.pl
+++ b/unix/mksyscall_solaris.pl
@@ -38,6 +38,11 @@ if($ARGV[0] =~ /^-/) {
 	exit 1;
 }
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 sub parseparamlist($) {
 	my ($list) = @_;
 	$list =~ s/^\s*//;
@@ -260,6 +265,8 @@ print <<EOF;
 // $cmdline
 // MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package $package
 
 import "unsafe"
diff --git a/unix/mksysctl_openbsd.pl b/unix/mksysctl_openbsd.pl
index 6f540ba8..be67afa4 100755
--- a/unix/mksysctl_openbsd.pl
+++ b/unix/mksysctl_openbsd.pl
@@ -14,6 +14,11 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $debug = 0;
 my %ctls = ();
 
@@ -237,6 +242,8 @@ print <<EOF;
 // mksysctl_openbsd.pl
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix;
 
 type mibentry struct {
diff --git a/unix/mksysnum_darwin.pl b/unix/mksysnum_darwin.pl
index 7601fbaa..d3e5147f 100755
--- a/unix/mksysnum_darwin.pl
+++ b/unix/mksysnum_darwin.pl
@@ -7,12 +7,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_darwin.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const (
diff --git a/unix/mksysnum_dragonfly.pl b/unix/mksysnum_dragonfly.pl
index 25df4d38..266a248c 100755
--- a/unix/mksysnum_dragonfly.pl
+++ b/unix/mksysnum_dragonfly.pl
@@ -8,12 +8,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_dragonfly.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const (
diff --git a/unix/mksysnum_freebsd.pl b/unix/mksysnum_freebsd.pl
index ea165a6f..b767e124 100755
--- a/unix/mksysnum_freebsd.pl
+++ b/unix/mksysnum_freebsd.pl
@@ -8,12 +8,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_freebsd.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const (
diff --git a/unix/mksysnum_linux.pl b/unix/mksysnum_linux.pl
index 8c8b22e6..4d4017de 100755
--- a/unix/mksysnum_linux.pl
+++ b/unix/mksysnum_linux.pl
@@ -5,12 +5,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_linux.pl ". join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const(
diff --git a/unix/mksysnum_netbsd.pl b/unix/mksysnum_netbsd.pl
index fc16fccb..e74616a6 100755
--- a/unix/mksysnum_netbsd.pl
+++ b/unix/mksysnum_netbsd.pl
@@ -8,12 +8,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_netbsd.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const (
diff --git a/unix/mksysnum_openbsd.pl b/unix/mksysnum_openbsd.pl
index 5dffa047..ae5aad58 100755
--- a/unix/mksysnum_openbsd.pl
+++ b/unix/mksysnum_openbsd.pl
@@ -8,12 +8,19 @@
 
 use strict;
 
+if($ENV{'GOARCH'} eq "" || $ENV{'GOOS'} eq "") {
+	print STDERR "GOARCH or GOOS not defined in environment\n";
+	exit 1;
+}
+
 my $command = "mksysnum_openbsd.pl " . join(' ', @ARGV);
 
 print <<EOF;
 // $command
 // MACHINE GENERATED BY THE ABOVE COMMAND; DO NOT EDIT
 
+// +build $ENV{'GOARCH'},$ENV{'GOOS'}
+
 package unix
 
 const (