diff --git a/poincare/include/poincare/tree_by_reference.h b/poincare/include/poincare/tree_by_reference.h
index 85eb29f19..925931256 100644
--- a/poincare/include/poincare/tree_by_reference.h
+++ b/poincare/include/poincare/tree_by_reference.h
@@ -53,7 +53,7 @@ public:
   int numberOfChildren() const { return node()->numberOfChildren(); }
   int indexOfChild(TreeByReference t) const { return node()->indexOfChild(t.node()); }
   TreeByReference parent() const { return (isUninitialized() || node()->parent() == nullptr) ? TreeByReference() : TreeByReference(node()->parent()); }
-  TreeByReference childAtIndex(int i) const { return TreeByReference(node()->childAtIndex(i)); }
+  TreeByReference childAtIndex(int i) const;
   void setParentIdentifier(int id) { node()->setParentIdentifier(id); }
   void deleteParentIdentifier() { node()->deleteParentIdentifier(); }
   void deleteParentIdentifierInChildren() { node()->deleteParentIdentifierInChildren(); }
diff --git a/poincare/src/tree_by_reference.cpp b/poincare/src/tree_by_reference.cpp
index 1fa4cfb37..44e24ba89 100644
--- a/poincare/src/tree_by_reference.cpp
+++ b/poincare/src/tree_by_reference.cpp
@@ -35,6 +35,8 @@ TreeByReference TreeByReference::clone() const {
 
 /* Hierarchy operations */
 
+TreeByReference TreeByReference::childAtIndex(int i) const { return TreeByReference(node()->childAtIndex(i)); }
+
 void TreeByReference::replaceWithInPlace(TreeByReference t) {
   assert(!isUninitialized());
   TreeByReference p = parent();