diff --git a/poincare/include/poincare/symbol.h b/poincare/include/poincare/symbol.h
index fd53292d9..a91cfabe5 100644
--- a/poincare/include/poincare/symbol.h
+++ b/poincare/include/poincare/symbol.h
@@ -70,6 +70,7 @@ public:
     return Expression();
   }
   // Symbol properties
+  bool isSystemSymbol() const { return name()[0] == SpecialSymbols::UnknownX && name()[1] == 0; }
   static bool isSeriesSymbol(const char * c);
   static bool isRegressionSymbol(const char * c);
   bool matches(ExpressionTest test, Context & context) const;
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index 5c21e6b5b..7c1c5b883 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -226,6 +226,7 @@ void Expression::defaultSetChildrenInPlace(Expression other) {
 bool Expression::hasReplaceableSymbols(Context & context) const {
   return recursivelyMatches([](const Expression e, Context & context, bool replaceSymbols) {
       return (e.type() == ExpressionNode::Type::Symbol
+          && !static_cast<const Symbol &>(e).isSystemSymbol()
           && !context.expressionForSymbol(static_cast<const Symbol &>(e)).isUninitialized())
       || (e.type() == ExpressionNode::Type::Function
            && !context.expressionForSymbol(static_cast<const Function &>(e)).isUninitialized());
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index ebb31f072..6454ef600 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -204,6 +204,9 @@ int Symbol::getPolynomialCoefficients(Context & context, const char * symbolName
 }
 
 Expression Symbol::replaceReplaceableSymbols(Context & context) {
+  if (isSystemSymbol()) {
+    return *this;
+  }
   Expression e = context.expressionForSymbol(*this);
   if (e.isUninitialized()) {
     return *this;