diff --git a/core/rawdb/accessors_chain.go b/core/rawdb/accessors_chain.go
index 0582e842c3..987b8df392 100644
--- a/core/rawdb/accessors_chain.go
+++ b/core/rawdb/accessors_chain.go
@@ -175,7 +175,9 @@ func WriteFinalizedBlockHash(db ethdb.KeyValueWriter, hash common.Hash) {
 }
 
 // ReadLastPivotNumber retrieves the number of the last pivot block. If the node
-// full synced, the last pivot will always be nil.
+// has never attempted snap sync, the last pivot will always be nil. The marker
+// is written during snap sync and never cleared, so that a rollback past the
+// pivot can re-enable snap sync.
 func ReadLastPivotNumber(db ethdb.KeyValueReader) *uint64 {
 	data, _ := db.Get(lastPivotKey)
 	if len(data) == 0 {