diff --git a/consensus/XDPoS/engines/engine_v2/snapshot.go b/consensus/XDPoS/engines/engine_v2/snapshot.go
index f0ce71a2d43..c080ffbd385 100644
--- a/consensus/XDPoS/engines/engine_v2/snapshot.go
+++ b/consensus/XDPoS/engines/engine_v2/snapshot.go
@@ -17,6 +17,7 @@ type SnapshotV2 struct {
 	Hash   common.Hash `json:"hash"`   // Block hash where the snapshot was created
 
 	// candidates will get assigned on updateM1
+	// NOTE: must keep JSON tag "masterNodes", ref: PR #517
 	NextEpochCandidates []common.Address `json:"masterNodes"` // Set of authorized candidates nodes at this moment for next epoch
 }