diff --git a/migrate/etcd4.go b/migrate/etcd4.go
index 2a2d57881..62aaeb4bd 100644
--- a/migrate/etcd4.go
+++ b/migrate/etcd4.go
@@ -29,6 +29,7 @@ import (
 	"github.com/coreos/etcd/wal/walpb"
 )
 
+// We need an offset in leader election terms, because term 0 is special in 2.0.
 const termOffset4to2 = 1
 
 func snapDir4(dataDir string) string {