diff --git a/consensus/src/units/mod.rs b/consensus/src/units/mod.rs
index d08ad22e..371d74c2 100644
--- a/consensus/src/units/mod.rs
+++ b/consensus/src/units/mod.rs
@@ -70,11 +70,8 @@ impl<H: Hasher> ControlHash<H> {
 
     /// Calculate parent control hash, which includes all parent hashes into account.
     pub(crate) fn combine_hashes(parent_map: &NodeMap<(H::Hash, Round)>) -> H::Hash {
-        // TODO test without excluding rounds
-        let mut parents_hashes = NodeMap::with_size(parent_map.size());
-        for (parent_index, &(hash, _)) in parent_map.iter() {
-            parents_hashes.insert(parent_index, hash);
-        }
+        // we include parent rounds with calculating hash but this is okay - we cannot 
+        // have two units with the same hash but different rounds
         parent_map.using_encoded(H::hash)
     }