diff --git a/source/Components/Xceed.Wpf.AvalonDock/Controls/LayoutFloatingWindowControl.cs b/source/Components/Xceed.Wpf.AvalonDock/Controls/LayoutFloatingWindowControl.cs
index badc94bd..1cf0da19 100644
--- a/source/Components/Xceed.Wpf.AvalonDock/Controls/LayoutFloatingWindowControl.cs
+++ b/source/Components/Xceed.Wpf.AvalonDock/Controls/LayoutFloatingWindowControl.cs
@@ -360,6 +360,13 @@ protected virtual IntPtr FilterMessage( IntPtr hwnd, int msg, IntPtr wParam, Int
 
     internal void InternalClose()
     {
+      // Check before Close in InternalClose
+      // https://github.com/xceedsoftware/wpftoolkit/issues/1310
+      if( _internalCloseFlag )
+      {
+        return;
+      }
+
       _internalCloseFlag = true;
       Close();
     }