diff --git a/poincare/include/poincare/number.h b/poincare/include/poincare/number.h
index aa4886f75..747d572f1 100644
--- a/poincare/include/poincare/number.h
+++ b/poincare/include/poincare/number.h
@@ -39,9 +39,9 @@ public:
    * account as it is not an internal node - it will always be turned into a
    * Rational/Float beforehand. */
   // TODO: Use references for Addition / Multiplication / Power
-  static Number Addition(const Number i, const Number j);
-  static Number Multiplication(const Number i, const Number j);
-  static Number Power(const Number i, const Number j);
+  static Number Addition(const Number & i, const Number & j);
+  static Number Multiplication(const Number & i, const Number & j);
+  static Number Power(const Number & i, const Number & j);
 protected:
   Number() : Expression() {}
   NumberNode * node() const override { return static_cast<NumberNode *>(Expression::node()); }
@@ -49,7 +49,7 @@ private:
   typedef Integer (*IntegerBinaryOperation)(const Integer & i, const Integer & j);
   typedef Rational (*RationalBinaryOperation)(const Rational & i, const Rational & j);
   typedef double (*DoubleBinaryOperation)(double i, double j);
-  static Number BinaryOperation(const Number i, const Number j, IntegerBinaryOperation integerOp, RationalBinaryOperation rationalOp, DoubleBinaryOperation doubleOp);
+  static Number BinaryOperation(const Number & i, const Number & j, IntegerBinaryOperation integerOp, RationalBinaryOperation rationalOp, DoubleBinaryOperation doubleOp);
 };
 
 }
diff --git a/poincare/src/number.cpp b/poincare/src/number.cpp
index 640b35faf..16e21d9c1 100644
--- a/poincare/src/number.cpp
+++ b/poincare/src/number.cpp
@@ -74,7 +74,7 @@ Number Number::FloatNumber(double d) {
   }
 }
 
-Number Number::BinaryOperation(const Number i, const Number j, IntegerBinaryOperation integerOp, RationalBinaryOperation rationalOp, DoubleBinaryOperation doubleOp) {
+Number Number::BinaryOperation(const Number & i, const Number & j, IntegerBinaryOperation integerOp, RationalBinaryOperation rationalOp, DoubleBinaryOperation doubleOp) {
   if (i.node()->type() == ExpressionNode::Type::Integer && j.node()->type() == ExpressionNode::Type::Integer) {
   // Integer + Integer
     Integer k = integerOp(Integer(static_cast<IntegerNode *>(i.node())), Integer(static_cast<IntegerNode *>(j.node())));
@@ -102,15 +102,15 @@ Number Number::BinaryOperation(const Number i, const Number j, IntegerBinaryOper
   return FloatNumber(a);
 }
 
-Number Number::Addition(const Number i, const Number j) {
+Number Number::Addition(const Number & i, const Number & j) {
   return BinaryOperation(i, j, Integer::Addition, Rational::Addition, [](double a, double b) { return a+b; });
 }
 
-Number Number::Multiplication(const Number i, const Number j) {
+Number Number::Multiplication(const Number & i, const Number & j) {
   return BinaryOperation(i, j, Integer::Multiplication, Rational::Multiplication, [](double a, double b) { return a*b; });
 }
 
-Number Number::Power(const Number i, const Number j) {
+Number Number::Power(const Number & i, const Number & j) {
   return BinaryOperation(i, j, Integer::Power,
       // Special case for Rational^Rational: we escape to Float if the index is not an Integer
       [](const Rational & i, const Rational & j) {