diff --git a/net/packet/tsmp.go b/net/packet/tsmp.go
index 790181244..182121eef 100644
--- a/net/packet/tsmp.go
+++ b/net/packet/tsmp.go
@@ -63,6 +63,7 @@ func (rh TailscaleRejectedHeader) String() string {
 	return fmt.Sprintf("TSMP-reject-flow{%s %s > %s}: %s", rh.Proto, rh.Src, rh.Dst, rh.Reason)
 }
 
+// TSMPType is the type byte of a TSMP message. It follows the IPv4 or IPv6 header.
 type TSMPType uint8
 
 const (