diff --git a/poincare/src/tree_handle.cpp b/poincare/src/tree_handle.cpp
index bc7429e61..3e87d6f7a 100644
--- a/poincare/src/tree_handle.cpp
+++ b/poincare/src/tree_handle.cpp
@@ -62,6 +62,7 @@ void TreeHandle::replaceChildInPlace(TreeHandle oldChild, TreeHandle newChild) {
   if (oldChild == newChild) {
     return;
   }
+  assert(!oldChild.hasAncestor(newChild, true));
 
   assert(!isUninitialized());