diff --git a/apps/sequence/sequence.h b/apps/sequence/sequence.h
index db28a2db6..97b5354d9 100644
--- a/apps/sequence/sequence.h
+++ b/apps/sequence/sequence.h
@@ -27,7 +27,6 @@ public:
     Function(record),
     m_nameLayout() {}
   CodePoint symbol() const override { return 'n'; }
-  CodePoint unknownSymbol() const override { return UCodePointUnknownX; }
   void tidy() override;
   // MetaData getters
   Type type() const;
diff --git a/apps/shared/cartesian_function.h b/apps/shared/cartesian_function.h
index f9d769a40..a671667f4 100644
--- a/apps/shared/cartesian_function.h
+++ b/apps/shared/cartesian_function.h
@@ -15,7 +15,6 @@ public:
     Function(record)
   {}
   CodePoint symbol() const override { return 'x'; }
-  CodePoint unknownSymbol() const override { return UCodePointUnknownX; }
 
   // Evaluation
   float evaluateAtAbscissa(float x, Poincare::Context * context) const override {
diff --git a/apps/shared/expression_model.cpp b/apps/shared/expression_model.cpp
index fe3794b75..13219378c 100644
--- a/apps/shared/expression_model.cpp
+++ b/apps/shared/expression_model.cpp
@@ -20,13 +20,13 @@ ExpressionModel::ExpressionModel() :
 {
 }
 
-void ExpressionModel::text(const Storage::Record * record, char * buffer, size_t bufferSize, CodePoint symbol, CodePoint unknownSymbol) const {
+void ExpressionModel::text(const Storage::Record * record, char * buffer, size_t bufferSize, CodePoint symbol) const {
   Expression e = expressionClone(record);
   if (e.isUninitialized() && bufferSize > 0) {
     buffer[0] = 0;
   } else {
     if (symbol != 0 && !e.isUninitialized()) {
-      e = e.replaceUnknown(Symbol::Builder(unknownSymbol), Symbol::Builder(symbol));
+      e = e.replaceUnknown(Symbol::Builder(UCodePointUnknownX), Symbol::Builder(symbol));
     }
     e.serialize(buffer, bufferSize);
   }
@@ -58,11 +58,11 @@ Expression ExpressionModel::expressionClone(const Storage::Record * record) cons
   return Expression::ExpressionFromAddress(expressionAddress(record), expressionSize(record));
 }
 
-Layout ExpressionModel::layout(const Storage::Record * record, CodePoint symbol, CodePoint unknownSymbol) const {
+Layout ExpressionModel::layout(const Storage::Record * record, CodePoint symbol) const {
   if (m_layout.isUninitialized()) {
     Expression clone = expressionClone(record);
     if (!clone.isUninitialized() && symbol != 0) {
-      clone = clone.replaceUnknown(Symbol::Builder(unknownSymbol), Symbol::Builder(symbol));
+      clone = clone.replaceUnknown(Symbol::Builder(UCodePointUnknownX), Symbol::Builder(symbol));
     }
     m_layout = PoincareHelpers::CreateLayout(clone);
     if (m_layout.isUninitialized()) {
@@ -72,8 +72,8 @@ Layout ExpressionModel::layout(const Storage::Record * record, CodePoint symbol,
   return m_layout;
 }
 
-Ion::Storage::Record::ErrorStatus ExpressionModel::setContent(Ion::Storage::Record * record, const char * c, CodePoint symbol, CodePoint unknownSymbol) {
-  Expression e = ExpressionModel::BuildExpressionFromText(c, symbol, unknownSymbol);
+Ion::Storage::Record::ErrorStatus ExpressionModel::setContent(Ion::Storage::Record * record, const char * c, CodePoint symbol) {
+  Expression e = ExpressionModel::BuildExpressionFromText(c, symbol);
   return setExpressionContent(record, e);
 }
 
@@ -122,14 +122,14 @@ void ExpressionModel::tidy() const {
   m_circular = 0;
 }
 
-Poincare::Expression ExpressionModel::BuildExpressionFromText(const char * c, char symbol, char unknownSymbol) {
+Poincare::Expression ExpressionModel::BuildExpressionFromText(const char * c, char symbol) {
   Expression expressionToStore;
   // if c = "", we want to reinit the Expression
   if (c && *c != 0) {
     // Compute the expression to store, without replacing symbols
     expressionToStore = Expression::Parse(c);
     if (!expressionToStore.isUninitialized() && symbol != 0) {
-      expressionToStore = expressionToStore.replaceUnknown(Symbol::Builder(symbol), Symbol::Builder(unknownSymbol));
+      expressionToStore = expressionToStore.replaceUnknown(Symbol::Builder(symbol), Symbol::Builder(UCodePointUnknownX));
     }
   }
   return expressionToStore;
diff --git a/apps/shared/expression_model.h b/apps/shared/expression_model.h
index cc2412f30..c04e7f297 100644
--- a/apps/shared/expression_model.h
+++ b/apps/shared/expression_model.h
@@ -12,13 +12,13 @@ public:
   ExpressionModel();
 
   // Getters
-  void text(const Ion::Storage::Record * record, char * buffer, size_t bufferSize, CodePoint symbol = 0, CodePoint unknownSymbol = 0) const;
+  void text(const Ion::Storage::Record * record, char * buffer, size_t bufferSize, CodePoint symbol = 0) const;
   Poincare::Expression expressionReduced(const Ion::Storage::Record * record, Poincare::Context * context) const;
   Poincare::Expression expressionClone(const Ion::Storage::Record * record) const;
-  Poincare::Layout layout(const Ion::Storage::Record * record, CodePoint symbol = 0, CodePoint unknownSymbol = 0) const;
+  Poincare::Layout layout(const Ion::Storage::Record * record, CodePoint symbol = 0) const;
 
   // Setters
-  Ion::Storage::Record::ErrorStatus setContent(Ion::Storage::Record * record, const char * c, CodePoint symbol = 0, CodePoint unknownSymbol = 0);
+  Ion::Storage::Record::ErrorStatus setContent(Ion::Storage::Record * record, const char * c, CodePoint symbol = 0);
   Ion::Storage::Record::ErrorStatus setExpressionContent(Ion::Storage::Record * record, Poincare::Expression & e);
 
   // Property
@@ -28,7 +28,7 @@ public:
   virtual void tidy() const;
 protected:
   // Setters helper
-  static Poincare::Expression BuildExpressionFromText(const char * c, char symbol = 0, char unknownSymbol = 0);
+  static Poincare::Expression BuildExpressionFromText(const char * c, char symbol = 0);
   mutable Poincare::Expression m_expression;
   mutable Poincare::Layout m_layout;
 private:
diff --git a/apps/shared/expression_model_handle.h b/apps/shared/expression_model_handle.h
index 298f4f74e..4284b0be3 100644
--- a/apps/shared/expression_model_handle.h
+++ b/apps/shared/expression_model_handle.h
@@ -11,13 +11,12 @@ class ExpressionModelHandle : public Ion::Storage::Record {
 public:
   ExpressionModelHandle(Ion::Storage::Record record = Ion::Storage::Record());
   virtual CodePoint symbol() const { return 0; }
-  virtual CodePoint unknownSymbol() const { return 0; }
 
   // Property
-  void text(char * buffer, size_t bufferSize) const { return model()->text(this, buffer, bufferSize, symbol(), unknownSymbol()); }
+  void text(char * buffer, size_t bufferSize) const { return model()->text(this, buffer, bufferSize, symbol()); }
   Poincare::Expression expressionReduced(Poincare::Context * context) const { return model()->expressionReduced(this, context); }
   Poincare::Expression expressionClone() const { return model()->expressionClone(this); }
-  Poincare::Layout layout() { return model()->layout(this, symbol(), unknownSymbol()); }
+  Poincare::Layout layout() { return model()->layout(this, symbol()); }
    /* Here, isDefined is the exact contrary of isEmpty. However, for Sequence
    * inheriting from ExpressionModelHandle, isEmpty and isDefined have not exactly
    * opposite meaning. For instance, u(n+1)=u(n) & u(0) = ... is not empty and
@@ -31,7 +30,7 @@ public:
    * behaviour but it is not true for its child classes (for example, in
    * Sequence). */
   virtual void tidy() { model()->tidy(); }
-  Ion::Storage::Record::ErrorStatus setContent(const char * c) { return editableModel()->setContent(this, c, symbol(), unknownSymbol()); }
+  Ion::Storage::Record::ErrorStatus setContent(const char * c) { return editableModel()->setContent(this, c, symbol()); }
   Ion::Storage::Record::ErrorStatus setExpressionContent(Poincare::Expression & e) { return editableModel()->setExpressionContent(this, e); }
 protected:
   bool isCircularlyDefined(Poincare::Context * context) const { return model()->isCircularlyDefined(this, context); }