diff --git a/wgengine/magicsock/discopingpurpose_string.go b/wgengine/magicsock/discopingpurpose_string.go
new file mode 100644
index 000000000..b835704e9
--- /dev/null
+++ b/wgengine/magicsock/discopingpurpose_string.go
@@ -0,0 +1,29 @@
+// Copyright (c) 2020 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.
+
+// Code generated by "stringer -type=discoPingPurpose -trimprefix=ping"; DO NOT EDIT.
+
+package magicsock
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[pingDiscovery-0]
+	_ = x[pingHeartbeat-1]
+	_ = x[pingCLI-2]
+}
+
+const _discoPingPurpose_name = "DiscoveryHeartbeatCLI"
+
+var _discoPingPurpose_index = [...]uint8{0, 9, 18, 21}
+
+func (i discoPingPurpose) String() string {
+	if i < 0 || i >= discoPingPurpose(len(_discoPingPurpose_index)-1) {
+		return "discoPingPurpose(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _discoPingPurpose_name[_discoPingPurpose_index[i]:_discoPingPurpose_index[i+1]]
+}
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 77926c95f..6ab027771 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -3465,6 +3465,7 @@ 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
 const (
 	// pingDiscovery means that purpose of a ping was to see if a
 	// path was valid.