diff --git a/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs b/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
index c40485f..f578f42 100644
--- a/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
+++ b/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
@@ -651,8 +651,19 @@
 
         private static object Fact(List<Expression> p)
         {
-            var num = Math.Floor(p[0]);
+            var input = p[0].Evaluate();
+
+            if (!(input is long || input is int || input is byte || input is double || input is float))
+                throw new CellValueException();
+
+
+            var num = Math.Floor((double)input);
             double fact = 1.0;
+
+            
+            if (num < 0)
+                throw new NumberException();
+
             if (num > 1)
                 for (int i = 2; i <= num; i++)
                     fact *= i;
diff --git a/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs b/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
index 5960ddf..72b10fe 100644
--- a/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
+++ b/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
@@ -784,6 +784,44 @@
             Assert.AreEqual(expectedResult, actual, tolerance);
         }
 
+        [TestCase(0, 1L)]
+        [TestCase(1, 1L)]
+        [TestCase(2, 2L)]
+        [TestCase(3, 6L)]
+        [TestCase(4, 24L)]
+        [TestCase(5, 120L)]
+        [TestCase(6, 720L)]
+        [TestCase(7, 5040L)]
+        [TestCase(8, 40320L)]
+        [TestCase(9, 362880L)]
+        [TestCase(10, 3628800L)]
+        [TestCase(11, 39916800L)]
+        [TestCase(12, 479001600L)]
+        [TestCase(13, 6227020800L)]
+        [TestCase(14, 87178291200L)]
+        [TestCase(15, 1307674368000L)]
+        [TestCase(16, 20922789888000L)]
+        [TestCase(0.1, 1L)]
+        [TestCase(2.3, 2L)]
+        [TestCase(2.8, 2L)]
+        public void Fact_ReturnsCorrectResult(double input, long expectedResult)
+        {
+            var actual = (double)XLWorkbook.EvaluateExpr(string.Format(@"FACT({0})", input.ToString(CultureInfo.InvariantCulture)));
+            Assert.AreEqual(expectedResult, actual);
+        }
+
+        [Theory]
+        public void Fact_ThrowsNumberExceptionForNegativeInput([Range(-10, -1)] int input)
+        {
+            Assert.Throws<NumberException>(() => XLWorkbook.EvaluateExpr(string.Format(@"FACT({0})", input.ToString(CultureInfo.InvariantCulture))));
+        }
+
+        [Test]
+        public void Fact_ThrowsValueExceptionForNonNumericInput()
+        {
+            Assert.Throws<CellValueException>(() => XLWorkbook.EvaluateExpr(string.Format(@"FACT(""x"")")));
+        }
+
         [Test]
         public void Floor()
         {