diff --git a/poincare/Makefile b/poincare/Makefile
index da0f614ec..937ee09e2 100644
--- a/poincare/Makefile
+++ b/poincare/Makefile
@@ -54,6 +54,7 @@ objs += $(addprefix poincare/src/,\
   division.o\
   division_quotient.o\
   division_remainder.o\
+  empty_expression.o\
   evaluation.o\
   expression.o\
   expression_lexer.o\
diff --git a/poincare/include/poincare.h b/poincare/include/poincare.h
index 4251de540..e294551d5 100644
--- a/poincare/include/poincare.h
+++ b/poincare/include/poincare.h
@@ -120,6 +120,7 @@
 #include <poincare/determinant.h>
 #include <poincare/division_quotient.h>
 #include <poincare/division_remainder.h>
+#include <poincare/empty_expression.h>
 #include <poincare/sine.h>
 #include <poincare/tangent.h>
 #include <poincare/hyperbolic_arc_cosine.h>
diff --git a/poincare/include/poincare/empty_expression.h b/poincare/include/poincare/empty_expression.h
index bf7830ac7..c2e5012d2 100644
--- a/poincare/include/poincare/empty_expression.h
+++ b/poincare/include/poincare/empty_expression.h
@@ -1,28 +1,45 @@
 #ifndef POINCARE_EMPTY_EXPRESSION_H
 #define POINCARE_EMPTY_EXPRESSION_H
 
-#include <poincare/static_hierarchy.h>
-#include <poincare/evaluation.h>
+#include <poincare/expression.h>
 
 namespace Poincare {
 
-/* An empty expression awaits completion by the user. */
+// An empty expression awaits completion by the user.
 
-class EmptyExpression : public StaticHierarchy<0> {
+class EmptyExpressionNode : public ExpressionNode  {
 public:
-  Type type() const override {
-    return Type::EmptyExpression;
+  // Allocation Failure
+  static EmptyExpressionNode * FailedAllocationStaticNode();
+  EmptyExpressionNode * failedAllocationStaticNode() override { return FailedAllocationStaticNode(); }
+
+  // TreeNode
+  size_t size() const override { return sizeof(EmptyExpressionNode); }
+  int numberOfChildren() const override { return 0; }
+#if POINCARE_TREE_LOG
+  virtual void logNodeName(std::ostream & stream) const override {
+    stream << "EmptyExpression";
   }
+#endif
+
+  // Properties
+  Type type() const override { return Type::EmptyExpression; }
   int serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
 private:
-  /* Layout */
-  LayoutRef createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
-  /* Evaluation */
+  // Layout
+  LayoutReference createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
+  // Evaluation
   Evaluation<float> approximate(SinglePrecision p, Context& context, Preferences::AngleUnit angleUnit) const override { return templatedApproximate<float>(context, angleUnit); }
   Evaluation<double> approximate(DoublePrecision p, Context& context, Preferences::AngleUnit angleUnit) const override { return templatedApproximate<double>(context, angleUnit); }
   template<typename T> Evaluation<T> templatedApproximate(Context& context, Preferences::AngleUnit angleUnit) const;
 };
 
+class EmptyExpression : public Expression {
+public:
+  EmptyExpression() : Expression(TreePool::sharedPool()->createTreeNode<EmptyExpressionNode>()) {}
+  EmptyExpression(const EmptyExpressionNode * n) : Expression(n) {}
+};
+
 }
 
 #endif
diff --git a/poincare/src/empty_expression.cpp b/poincare/src/empty_expression.cpp
index c27247ca4..fb324553e 100644
--- a/poincare/src/empty_expression.cpp
+++ b/poincare/src/empty_expression.cpp
@@ -1,25 +1,28 @@
 #include <poincare/empty_expression.h>
+#include <poincare/allocation_failure_expression_node.h>
+#include <poincare/complex.h>
 #include <poincare/empty_layout_node.h>
-#include <poincare/layout_helper.h>
+#include <poincare/serialization_helper.h>
 #include <ion/charset.h>
-#include <math.h>
 
 namespace Poincare {
 
-Expression * EmptyExpression::clone() const {
-  return new EmptyExpression();
+EmptyExpressionNode * EmptyExpressionNode::FailedAllocationStaticNode() {
+  static AllocationFailureExpressionNode<EmptyExpressionNode> failure;
+  TreePool::sharedPool()->registerStaticNodeIfRequired(&failure);
+  return &failure;
 }
 
-int EmptyExpression::serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
+int EmptyExpressionNode::serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
   return SerializationHelper::Char(buffer, bufferSize, Ion::Charset::Empty);
 }
 
-LayoutRef EmptyExpression::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
+LayoutRef EmptyExpressionNode::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
   return EmptyLayoutRef();
 }
 
-template<typename T> Complex<T> * EmptyExpression::templatedApproximate(Context& context, Preferences::AngleUnit angleUnit) const {
-  return new Complex<T>(Complex<T>::Undefined());
+template<typename T> Evaluation<T> EmptyExpressionNode::templatedApproximate(Context& context, Preferences::AngleUnit angleUnit) const {
+  return Complex<T>::Undefined();
 }
 
 }
diff --git a/poincare/src/expression_lexer.l b/poincare/src/expression_lexer.l
index 53b03f49d..ab558f35e 100644
--- a/poincare/src/expression_lexer.l
+++ b/poincare/src/expression_lexer.l
@@ -189,10 +189,7 @@ inf { poincare_expression_yylval.expression = Undefined(); return UNDEFINED; }
 \] { return RIGHT_BRACKET; }
 \, { return COMMA; }
 \_ { return UNDERSCORE; }
- /*
-\x97 { poincare_expression_yylval.expression = new EmptyExpression(); return EMPTY; }
- */
-
+\x97 { poincare_expression_yylval.expression = EmptyExpression(); return EMPTY; }
 [ ]+ /* Ignore whitespaces */
 . { return UNDEFINED_SYMBOL; }