diff --git a/cmd/addlicense/main.go b/cmd/addlicense/main.go
new file mode 100644
index 000000000..0ca9dc5de
--- /dev/null
+++ b/cmd/addlicense/main.go
@@ -0,0 +1,77 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Program addlicense adds a license header to a file.
+// It is intended for use with 'go generate',
+// so it has a slightly weird usage.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+var (
+	year = flag.Int("year", 0, "copyright year")
+	file = flag.String("file", "", "file to modify")
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, `
+usage: addlicense -year YEAR -file FILE <subcommand args...>
+`[1:])
+
+	flag.PrintDefaults()
+	fmt.Fprintf(os.Stderr, `
+addlicense adds a Tailscale license to the beginning of file,
+using year as the copyright year.
+
+It is intended for use with 'go generate', so it also runs a subcommand,
+which presumably creates the file.
+
+Sample usage:
+
+addlicense -year 2021 -file pull_strings.go stringer -type=pull
+`[1:])
+	os.Exit(2)
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+	if len(flag.Args()) == 0 {
+		flag.Usage()
+	}
+	cmd := exec.Command(flag.Arg(0), flag.Args()[1:]...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	check(err)
+	b, err := os.ReadFile(*file)
+	check(err)
+	f, err := os.OpenFile(*file, os.O_TRUNC|os.O_WRONLY, 0644)
+	check(err)
+	_, err = fmt.Fprintf(f, license, *year)
+	check(err)
+	_, err = f.Write(b)
+	check(err)
+	err = f.Close()
+	check(err)
+}
+
+func check(err error) {
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+var license = `
+// Copyright (c) %d Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+`[1:]
diff --git a/derp/derp_server.go b/derp/derp_server.go
index 32b09fb7b..70957a138 100644
--- a/derp/derp_server.go
+++ b/derp/derp_server.go
@@ -698,7 +698,7 @@ func (c *sclient) handleFrameSendPacket(ft frameType, fl uint32) error {
 // dropReason is why we dropped a DERP frame.
 type dropReason int
 
-//go:generate stringer -type=dropReason -trimprefix=dropReason
+//go:generate go run tailscale.com/cmd/addlicense -year 2021 -file dropreason_string.go stringer -type=dropReason -trimprefix=dropReason
 
 const (
 	dropReasonUnknownDest      dropReason = iota // unknown destination pubkey
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index a3b89759d..220ffebf7 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -3489,7 +3489,7 @@ func (de *discoEndpoint) sendDiscoPing(ep netaddr.IPPort, txid stun.TxID, logLev
 // discoPingPurpose is the reason why a discovery ping message was sent.
 type discoPingPurpose int
 
-//go:generate stringer -type=discoPingPurpose -trimprefix=ping
+//go:generate go run tailscale.com/cmd/addlicense -year 2020 -file discopingpurpose_string.go stringer -type=discoPingPurpose -trimprefix=ping
 const (
 	// pingDiscovery means that purpose of a ping was to see if a
 	// path was valid.