diff --git a/source/Components/AvalonDock/DockingManager.cs b/source/Components/AvalonDock/DockingManager.cs
index e1d46907..0811b7a5 100644
--- a/source/Components/AvalonDock/DockingManager.cs
+++ b/source/Components/AvalonDock/DockingManager.cs
@@ -2343,7 +2343,7 @@ private void Layout_ElementRemoved(object sender, LayoutElementEventArgs e)
 		private void Layout_ElementAdded(object sender, LayoutElementEventArgs e)
 		{
 			if (_suspendLayoutItemCreation) return;
-			foreach (var content in Layout.Descendents().OfType<LayoutContent>())
+			foreach (var content in Layout.Descendents().OfType<LayoutContent>().ToList())
 			{
 				if (content is LayoutDocument)
 					CreateDocumentLayoutItem(content as LayoutDocument);