diff --git a/Assets/Fungus/Docs/CHANGELOG.txt b/Assets/Fungus/Docs/CHANGELOG.txt
index 232c3146..fd5ef1ed 100644
--- a/Assets/Fungus/Docs/CHANGELOG.txt
+++ b/Assets/Fungus/Docs/CHANGELOG.txt
@@ -5,6 +5,7 @@ Unreleased
 ======
 ## Fixed
  - Add missing VariableDrawer for ObjectVariable. Thanks to CG-Tespy.
+ - Fix double duplication of blocks in flowchart window. Thanks to ongjinwen.
  
 ## Changed
  - Block will LogError when an exception is caught from a Command being Executed.
diff --git a/Assets/Fungus/Scripts/Editor/FlowchartWindow.cs b/Assets/Fungus/Scripts/Editor/FlowchartWindow.cs
index d5a9b6bf..7bcd90fe 100644
--- a/Assets/Fungus/Scripts/Editor/FlowchartWindow.cs
+++ b/Assets/Fungus/Scripts/Editor/FlowchartWindow.cs
@@ -1895,11 +1895,8 @@ namespace Fungus.EditorUtils
         {
             copyList.Clear();
 
-            foreach (var block in flowchart.SelectedBlocks)
-            {
-                copyList.Add(new BlockCopy(block));
-            }
-            foreach (var block in mouseDownSelectionState)
+            foreach (var block in flowchart.SelectedBlocks
+                .Union(mouseDownSelectionState))
             {
                 copyList.Add(new BlockCopy(block));
             }