diff --git a/poincare/include/poincare/tree_node.h b/poincare/include/poincare/tree_node.h
index 8eb766f55..28172ff8f 100644
--- a/poincare/include/poincare/tree_node.h
+++ b/poincare/include/poincare/tree_node.h
@@ -22,11 +22,12 @@ public:
   virtual ~TreeNode() {}
 
   // Attributes
+  bool isStatic() const;
   virtual size_t size() const = 0;
   int identifier() const { return m_identifier; }
   int retainCount() const { return m_referenceCounter; }
   void setReferenceCounter(int refCount) { //TODO make this method privte with only friends that can access it
-    if (m_identifier < 0) {
+    if (isStatic()) {
       // Do not retain static nodes
       return;
     }
@@ -51,7 +52,7 @@ public:
 
   // Node operations
   void retain() {
-    if (m_identifier < 0) {
+    if (isStatic()) {
       // Do not retain static nodes
       return;
     }
@@ -156,11 +157,7 @@ public:
   }
 
 protected:
-  TreeNode() :
-    m_identifier(-1),
-    m_referenceCounter(1)
-  {
-  }
+  TreeNode();
 
   TreeNode * lastChild() const {
     if (numberOfChildren() == 0) {
diff --git a/poincare/include/poincare/tree_pool.h b/poincare/include/poincare/tree_pool.h
index 11392a421..00d549714 100644
--- a/poincare/include/poincare/tree_pool.h
+++ b/poincare/include/poincare/tree_pool.h
@@ -12,6 +12,8 @@ class TreePool {
   friend class TreeNode;
 public:
   static constexpr int NoNodeIdentifier = -1;
+  static constexpr int FirstStaticNodeIdentifier = -2;
+
   static TreePool * sharedPool();
 
   // Node
@@ -108,8 +110,8 @@ private:
     node->rename(generateIdentifier(), unregisterPreviousIdentifier);
   }
 
-  int identifierOfStaticNodeAtIndex(int index) const { return - (index+2);} // We do not want positive indexes that are reserved for pool nodes, and -1 is reserved for node initialisation.
-  int indexOfStaticNode(int id) const { return -id-2;}
+  int identifierOfStaticNodeAtIndex(int index) const { return FirstStaticNodeIdentifier-index;} // We do not want positive indexes that are reserved for pool nodes, and -1 is reserved for node initialisation.
+  int indexOfStaticNode(int id) const { return -(id - FirstStaticNodeIdentifier);}
 
   // Iterators
 
diff --git a/poincare/src/tree_node.cpp b/poincare/src/tree_node.cpp
index 0b00571d2..8a93ac1e0 100644
--- a/poincare/src/tree_node.cpp
+++ b/poincare/src/tree_node.cpp
@@ -5,10 +5,14 @@
 
 namespace Poincare {
 
+bool TreeNode::isStatic() const {
+  return m_identifier <= TreePool::FirstStaticNodeIdentifier;
+}
+
 // Node operations
 
 void TreeNode::release() {
-  if (m_identifier < 0) {
+  if (isStatic()) {
     // Do not release static nodes
     return;
   }
@@ -46,6 +50,9 @@ void TreeNode::rename(int identifier, bool unregisterPreviousIdentifier) {
 // Hierarchy
 
 TreeNode * TreeNode::parent() const {
+  if (isStatic()) {
+    return nullptr;
+  }
   /* Choose between these algorithms: the first has complexity O(numberNodes)
    * but uses O(3maxNumberNodes) space. The second is much clearer for the
    * reader and uses no space, but has complexity O(numberNodes^2) */
@@ -93,6 +100,9 @@ TreeNode * TreeNode::parent() const {
 }
 
 TreeNode * TreeNode::root() {
+  if (isStatic()) {
+    return this;
+  }
   for (TreeNode * root : TreePool::sharedPool()->roots()) {
     if (hasAncestor(root, true)) {
       return root;
@@ -192,6 +202,13 @@ bool TreeNode::hasSibling(const TreeNode * e) const {
   return false;
 }
 
+TreeNode::TreeNode() :
+  m_identifier(TreePool::NoNodeIdentifier),
+  m_referenceCounter(1)
+{
+}
+
+
 size_t TreeNode::deepSize(int realNumberOfChildren) const {
   if (realNumberOfChildren == -1) {
     // TODO: Error handling