diff --git a/Orm/Xtensive.Orm/Orm/Linq/Translator.Queryable.cs b/Orm/Xtensive.Orm/Orm/Linq/Translator.Queryable.cs
index 7f9aad345..e96cf1e4a 100644
--- a/Orm/Xtensive.Orm/Orm/Linq/Translator.Queryable.cs
+++ b/Orm/Xtensive.Orm/Orm/Linq/Translator.Queryable.cs
@@ -1253,7 +1253,10 @@ private ProjectionExpression CombineProjections(ProjectionExpression outer, Proj
     {
       var outerDataSource = outer.ItemProjector.DataSource;
       var outerLength = outerDataSource.Header.Length;
-      var tupleParameterBindings = outer.TupleParameterBindings.Union(inner.TupleParameterBindings).ToDictionary(pair => pair.Key, pair => pair.Value);
+      Dictionary<Parameter<Tuple>, Tuple> tupleParameterBindings = new(outer.TupleParameterBindings);
+      foreach (var pair in inner.TupleParameterBindings) {
+        tupleParameterBindings.TryAdd(pair.Key, pair.Value);
+      }
       outer = new ProjectionExpression(outer.Type, outer.ItemProjector.Remap(recordQuery, 0), tupleParameterBindings);
       inner = new ProjectionExpression(inner.Type, inner.ItemProjector.Remap(recordQuery, outerLength), tupleParameterBindings);