diff --git a/Orm/Xtensive.Orm/Collections/FlagCollection.cs b/Orm/Xtensive.Orm/Collections/FlagCollection.cs
index ca7ee8a0d..e73469b8f 100644
--- a/Orm/Xtensive.Orm/Collections/FlagCollection.cs
+++ b/Orm/Xtensive.Orm/Collections/FlagCollection.cs
@@ -232,15 +232,12 @@ bool ICollection<KeyValuePair<TKey, TFlag>>.Contains(KeyValuePair<TKey, TFlag> i
     /// <inheritdoc/>
     public IEnumerator<KeyValuePair<TKey, TFlag>> GetEnumerator()
     {
-      for (int i = 0; i < keys.Count; i++)
+      for (int i = 0, count = keys.Count; i < count; i++)
         yield return new KeyValuePair<TKey, TFlag>(keys[i], Converter.ConvertBackward(flags[1 << i]));
     }
 
     /// <inheritdoc/>
-    IEnumerator IEnumerable.GetEnumerator()
-    {
-      return ((IEnumerable<KeyValuePair<TKey, TFlag>>)this).GetEnumerator();
-    }
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
 
     #endregion
 
diff --git a/Orm/Xtensive.Orm/Orm/Rse/RecordSetHeader.cs b/Orm/Xtensive.Orm/Orm/Rse/RecordSetHeader.cs
index fecfb9a22..5b9ce0536 100644
--- a/Orm/Xtensive.Orm/Orm/Rse/RecordSetHeader.cs
+++ b/Orm/Xtensive.Orm/Orm/Rse/RecordSetHeader.cs
@@ -4,7 +4,6 @@
 // Created by: Alexey Kochetov
 // Created:    2007.09.13
 
-using System.Buffers;
 using Xtensive.Collections;
 using Xtensive.Core;
 using Xtensive.Orm.Model;
@@ -20,6 +19,8 @@ namespace Xtensive.Orm.Rse
   [Serializable]
   public sealed class RecordSetHeader
   {
+    private static readonly DirectionCollection<ColNum> EmptyOrder = new();
+
     private TupleDescriptor orderTupleDescriptor;
 
     /// <summary>
@@ -344,8 +345,17 @@ public RecordSetHeader(
 
       ColumnGroups = columnGroups ?? [];
       orderTupleDescriptor = orderKeyDescriptor ?? TupleDescriptor.Empty;
-      Order = order ?? new DirectionCollection<ColNum>();
-      Order.Lock(true);
+      if (order != null) {
+        (Order = order).Lock();
+      }
+      else {
+        Order = EmptyOrder;
+      }
+    }
+
+    static RecordSetHeader()
+    {
+      EmptyOrder.Lock();
     }
   }
 }