diff --git a/poincare/src/integer.cpp b/poincare/src/integer.cpp
index 7cea3ac8b..45366ccb7 100644
--- a/poincare/src/integer.cpp
+++ b/poincare/src/integer.cpp
@@ -336,7 +336,7 @@ Integer NaturalIntegerAbstract::upow(const NaturalIntegerAbstract * i, const Nat
 Integer NaturalIntegerAbstract::ufact(const NaturalIntegerAbstract * i) {
   Integer j(2);
   Integer result(1);
-  while (ucmp(i,j.node()) > 0) {
+  while (ucmp(i,j.node()) >= 0) {
     result = Integer::Multiplication(j, result);
     j = Integer::Addition(j, Integer(1));
   }
diff --git a/poincare/test/integer.cpp b/poincare/test/integer.cpp
index 1af43b561..dde5daa5f 100644
--- a/poincare/test/integer.cpp
+++ b/poincare/test/integer.cpp
@@ -197,6 +197,14 @@ QUIZ_CASE(poincare_integer_pow) {
   assert_pow_to(Integer("12345678910111213141516171819202122232425"), Integer(2), Integer("152415787751564791571474464067365843004067618915106260955633159458990465721380625"));
 }
 
+static inline void assert_factorial_to(const Integer i, const Integer j) {
+  assert(Integer::NaturalOrder(Integer::Factorial(i), j) == 0);
+}
+
+QUIZ_CASE(poincare_integer_factorial) {
+  assert_factorial_to(Integer(5), Integer(120));
+  assert_factorial_to(Integer(123), Integer("12146304367025329675766243241881295855454217088483382315328918161829235892362167668831156960612640202170735835221294047782591091570411651472186029519906261646730733907419814952960000000000000000000000000000"));
+}
 
 // Simplify 
 template<typename T>