diff --git a/ILSpy/TreeNodes/DerivedTypesTreeNode.cs b/ILSpy/TreeNodes/DerivedTypesTreeNode.cs
index 74344a4d0..58a91e90c 100644
--- a/ILSpy/TreeNodes/DerivedTypesTreeNode.cs
+++ b/ILSpy/TreeNodes/DerivedTypesTreeNode.cs
@@ -87,6 +87,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		{
 			this.def = def;
 			this.assemblies = assemblies;
+			this.LazyLoading = true;
 			threading = new ThreadingSupport();
 		}