diff --git a/lib/src/sortedmap.dart b/lib/src/sortedmap.dart
index 5a5db24..36eac64 100644
--- a/lib/src/sortedmap.dart
+++ b/lib/src/sortedmap.dart
@@ -210,8 +210,12 @@ class _SortedMap<K extends Comparable, V> extends MapBase<K, V>
       return;
     }
     if (this is! FilteredMap) {
-      _sortedEntries
-          .addAll(other.entries.map((e) => ordering.mapEntry(e.key, e.value)));
+      var entries = other.entries;
+      if (entries is! Iterable<_MapEntryWithIndex<K, V>>) {
+        entries = entries.map<_MapEntryWithIndex<K, V>>(
+            (e) => ordering.mapEntry(e.key, e.value));
+      }
+      _sortedEntries.addAll(entries);
       _map.addAll(other);
       return;
     }
diff --git a/lib/src/treeset.dart b/lib/src/treeset.dart
index 5aa44ba..fc0e2a9 100644
--- a/lib/src/treeset.dart
+++ b/lib/src/treeset.dart
@@ -393,10 +393,12 @@ class AvlTreeSet<V> extends _BaseTreeSet<V> {
         identical((items as dynamic).comparator, comparator)) {
       _root = items._root;
       return _root != null;
-    }
-    if (_root == null) {
-      //
-      var l = items.toList()..sort(comparator);
+    } else if (_root == null) {
+      var l = items.toList();
+      if (items is! TreeSet<V> ||
+          !identical((items as dynamic).comparator, comparator)) {
+        l.sort(comparator);
+      }
       _root = AvlNode.fromOrderedList(l);
       return true;
     }