diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java
index 93518aa8c4..ea8f69239e 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java	
+++ b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java	
@@ -3366,7 +3366,8 @@ void _setItemCount (TreeItem parentItem, long parentIter, List<TreeItem> items,
 				try {
 					for (int i = oldSize; i < count; i++) {
 						GTK.gtk_tree_store_insert_after (modelHandle, createdIter, parentIter, i == 0 ? 0 : modificationIter);
-						new TreeItem (this, parentItem, SWT.NONE, i, createdIter);
+						TreeItem result = new TreeItem (this, parentItem, SWT.NONE, i, createdIter);
+						assert items.get(i) == result : "TreeItem should self-insert into sibling list";
 						C.memmove (modificationIter, createdIter, GTK.GtkTreeIter_sizeof ());
 					}
 				} finally {