diff --git a/db/memtable.cc b/db/memtable.cc
index 287afdb..8cefcae 100644
--- a/db/memtable.cc
+++ b/db/memtable.cc
@@ -85,6 +85,7 @@ void MemTable::Add(SequenceNumber s, ValueType type,
   // Format of an entry is concatenation of:
   //  key_size     : varint32 of internal_key.size()
   //  key bytes    : char[internal_key.size()]
+  //    tag        : uint64((sequence << 8) | type)
   //  value_size   : varint32 of value.size()
   //  value bytes  : char[value.size()]
   size_t key_size = key.size();