diff --git a/poincare/include/poincare/opposite.h b/poincare/include/poincare/opposite.h
index f19ea55e1..809aa4c43 100644
--- a/poincare/include/poincare/opposite.h
+++ b/poincare/include/poincare/opposite.h
@@ -13,6 +13,7 @@ public:
   Expression * clone() const override;
   Type type() const override;
   int polynomialDegree(char symbolName) const override;
+  Sign sign() const override;
   template<typename T> static Complex<T> compute(const Complex<T> c, AngleUnit angleUnit);
 private:
   /* Layout */
diff --git a/poincare/src/opposite.cpp b/poincare/src/opposite.cpp
index a20245e23..a394e6f4f 100644
--- a/poincare/src/opposite.cpp
+++ b/poincare/src/opposite.cpp
@@ -27,6 +27,16 @@ int Opposite::polynomialDegree(char symbolName) const {
   return operand(0)->polynomialDegree(symbolName);
 }
 
+Expression::Sign Opposite::sign() const {
+  if (operand(0)->sign() == Sign::Positive) {
+    return Sign::Negative;
+  }
+  if (operand(0)->sign() == Sign::Negative) {
+    return Sign::Positive;
+  }
+  return Sign::Unknown;
+}
+
 /* Layout */
 
 bool Opposite::needParenthesisWithParent(const Expression * e) const {
diff --git a/poincare/test/properties.cpp b/poincare/test/properties.cpp
index e19c2250d..ab8dffefb 100644
--- a/poincare/test/properties.cpp
+++ b/poincare/test/properties.cpp
@@ -6,6 +6,34 @@
 
 using namespace Poincare;
 
+constexpr Poincare::Expression::Sign Positive = Poincare::Expression::Sign::Positive;
+constexpr Poincare::Expression::Sign Negative = Poincare::Expression::Sign::Negative;
+constexpr Poincare::Expression::Sign Unknown = Poincare::Expression::Sign::Unknown;
+
+void assert_parsed_expression_sign(const char * expression, Poincare::Expression::Sign sign) {
+  GlobalContext globalContext;
+  Expression * e = parse_expression(expression);
+  Expression::Simplify(&e, globalContext);
+  assert(e->sign() == sign);
+  delete e;
+}
+
+QUIZ_CASE(poincare_sign) {
+  assert_parsed_expression_sign("abs(-cos(2))", Positive);
+  assert_parsed_expression_sign("2.345E-23", Positive);
+  assert_parsed_expression_sign("-2.345E-23", Negative);
+  assert_parsed_expression_sign("2*(-3)*abs(-32)", Negative);
+  assert_parsed_expression_sign("2*(-3)*abs(-32)*cos(3)", Unknown);
+  assert_parsed_expression_sign("2^(-abs(3))", Positive);
+  assert_parsed_expression_sign("(-2)^4", Positive);
+  assert_parsed_expression_sign("(-2)^3", Negative);
+  assert_parsed_expression_sign("random()", Positive);
+  assert_parsed_expression_sign("42/3", Positive);
+  assert_parsed_expression_sign("-23/32", Negative);
+  assert_parsed_expression_sign("P", Positive);
+  assert_parsed_expression_sign("X", Positive);
+}
+
 QUIZ_CASE(poincare_polynomial_degree) {
   assert_parsed_expression_polynomial_degree("x+1", 1);
   assert_parsed_expression_polynomial_degree("cos(2)+1", 0);