diff --git a/poincare/include/poincare/layout_reference.h b/poincare/include/poincare/layout_reference.h
index 978f6d77d..1bc60971d 100644
--- a/poincare/include/poincare/layout_reference.h
+++ b/poincare/include/poincare/layout_reference.h
@@ -44,6 +44,7 @@ public:
   bool mustHaveLeftSibling() const { return const_cast<LayoutReference *>(this)->node()->mustHaveLeftSibling(); }
   bool isEmpty() const { return const_cast<LayoutReference *>(this)->node()->isEmpty(); }
   bool isHorizontal() const { return const_cast<LayoutReference *>(this)->node()->isHorizontal(); }
+  bool isMatrix() const { return const_cast<LayoutReference *>(this)->node()->isMatrix(); }
   bool isVerticalOffset() const { return const_cast<LayoutReference *>(this)->node()->isVerticalOffset(); }
   bool isLeftParenthesis() const { return const_cast<LayoutReference *>(this)->node()->isLeftParenthesis(); }
   bool isCollapsable(int * numberOfOpenParenthesis, bool goingLeft) const { return const_cast<LayoutReference *>(this)->node()->isCollapsable(numberOfOpenParenthesis, goingLeft); }
diff --git a/poincare/src/layout_node.cpp b/poincare/src/layout_node.cpp
index 77398a718..b5f3350e7 100644
--- a/poincare/src/layout_node.cpp
+++ b/poincare/src/layout_node.cpp
@@ -255,17 +255,17 @@ void LayoutNode::scoreCursorInDescendantsVertically (
 
 bool LayoutNode::changeGreySquaresOfAllMatrixAncestors(bool add) {
   bool changedSquares = false;
-  LayoutNode * currentAncestor = parent();
-  while (currentAncestor != nullptr) {
-    if (currentAncestor->isMatrix()) {
+  LayoutRef currentAncestor = LayoutRef(parent());
+  while (currentAncestor.isDefined()) {
+    if (currentAncestor.isMatrix()) {
       if (add) {
-        static_cast<MatrixLayoutNode *>(currentAncestor)->addGreySquares();
+        static_cast<MatrixLayoutNode *>(currentAncestor.node())->addGreySquares();
       } else {
-        static_cast<MatrixLayoutNode *>(currentAncestor)->removeGreySquares();
+        static_cast<MatrixLayoutNode *>(currentAncestor.node())->removeGreySquares();
       }
       changedSquares = true;
     }
-    currentAncestor = currentAncestor->parent();
+    currentAncestor = currentAncestor.parent();
   }
   return changedSquares;
 }