diff --git a/poincare/include/poincare/factor.h b/poincare/include/poincare/factor.h
index 922d6e0b7..7f8dc7668 100644
--- a/poincare/include/poincare/factor.h
+++ b/poincare/include/poincare/factor.h
@@ -33,9 +33,7 @@ private:
   /* Evaluation */
   Evaluation<float> approximate(SinglePrecision p, Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const override { return templatedApproximate<float>(context, complexFormat, angleUnit); }
   Evaluation<double> approximate(DoublePrecision p, Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const override { return templatedApproximate<double>(context, complexFormat, angleUnit); }
-  template<typename T> Evaluation<T> templatedApproximate(Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const {
-    return childAtIndex(0)->approximate(T(), context, complexFormat, angleUnit);
-  }
+  template<typename T> Evaluation<T> templatedApproximate(Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const;
 };
 
 class Factor final : public Expression {
diff --git a/poincare/src/factor.cpp b/poincare/src/factor.cpp
index 2d0c5e982..3e0297c12 100644
--- a/poincare/src/factor.cpp
+++ b/poincare/src/factor.cpp
@@ -35,6 +35,17 @@ Expression FactorNode::shallowBeautify(ReductionContext reductionContext) {
   return Factor(this).shallowBeautify(reductionContext);
 }
 
+// Add tests :)
+template<typename T>
+Evaluation<T> FactorNode::templatedApproximate(Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const {
+  Evaluation<T> e = childAtIndex(0)->approximate(T(), context, complexFormat, angleUnit);
+  if (std::isnan(e.toScalar())) {
+    return Complex<T>::Undefined();
+  }
+  return e;
+}
+
+
 Multiplication Factor::createMultiplicationOfIntegerPrimeDecomposition(Integer i, Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const {
   assert(!i.isZero());
   assert(!i.isNegative());
diff --git a/poincare/test/approximation.cpp b/poincare/test/approximation.cpp
index 46629f390..89bc3b8ac 100644
--- a/poincare/test/approximation.cpp
+++ b/poincare/test/approximation.cpp
@@ -343,6 +343,7 @@ QUIZ_CASE(poincare_approximation_function) {
 
   assert_expression_approximates_to<float>("factor(-23/4)", "-5.75");
   assert_expression_approximates_to<double>("factor(-123/24)", "-5.125");
+  assert_expression_approximates_to<float>("factor(𝐢)", "undef");
 
   assert_expression_approximates_to<float>("inverse([[1,2,3][4,5,-6][7,8,9]])", "[[-1.2917,-0.083333,0.375][1.0833,0.16667,-0.25][0.041667,-0.083333,0.041667]]", Degree, Cartesian, 5); // inverse is not precise enough to display 7 significative digits
   assert_expression_approximates_to<double>("inverse([[1,2,3][4,5,-6][7,8,9]])", "[[-1.2916666666667,-8.3333333333333ᴇ-2,0.375][1.0833333333333,1.6666666666667ᴇ-1,-0.25][4.1666666666667ᴇ-2,-8.3333333333333ᴇ-2,4.1666666666667ᴇ-2]]");
diff --git a/poincare/test/simplification.cpp b/poincare/test/simplification.cpp
index 828f6f204..82aff5136 100644
--- a/poincare/test/simplification.cpp
+++ b/poincare/test/simplification.cpp
@@ -362,6 +362,7 @@ QUIZ_CASE(poincare_simplification_function) {
   assert_parsed_expression_simplify_to("factor(1008/6895)", "\u00122^4×3^2\u0013/\u00125×197\u0013");
   assert_parsed_expression_simplify_to("factor(10007)", "10007");
   assert_parsed_expression_simplify_to("factor(10007^2)", Undefined::Name());
+  assert_parsed_expression_simplify_to("factor(𝐢)", Undefined::Name());
   assert_parsed_expression_simplify_to("floor(-1.3)", "-2");
   assert_parsed_expression_simplify_to("floor(2π)", "6");
   assert_parsed_expression_simplify_to("floor(123456789012345678901234567892/3)", "41152263004115226300411522630");