diff --git a/src/Perspex.Diagnostics/ViewModels/TreeNode.cs b/src/Perspex.Diagnostics/ViewModels/TreeNode.cs
index 7caf3ac075..2ecb1939b7 100644
--- a/src/Perspex.Diagnostics/ViewModels/TreeNode.cs
+++ b/src/Perspex.Diagnostics/ViewModels/TreeNode.cs
@@ -21,7 +21,7 @@ namespace Perspex.Diagnostics.ViewModels
 
             var classesChanged = Observable.FromEventPattern<
                     NotifyCollectionChangedEventHandler, 
-                    NotifyCollectionChangedEventHandler>(
+                    NotifyCollectionChangedEventArgs>(
                 x => control.Classes.CollectionChanged += x,
                 x => control.Classes.CollectionChanged -= x);