diff --git a/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs b/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
index b672b9a..b729b28 100644
--- a/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
+++ b/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
@@ -65,6 +65,7 @@
             ce.RegisterFunction("ROUND", 2, Round);
             ce.RegisterFunction("ROUNDDOWN", 2, RoundDown);
             ce.RegisterFunction("ROUNDUP", 1, 2, RoundUp);
+            ce.RegisterFunction("SEC", 1, Sec);
             ce.RegisterFunction("SERIESSUM", 4, SeriesSum);
             ce.RegisterFunction("SIGN", 1, Sign);
             ce.RegisterFunction("SIN", 1, Sin);
@@ -742,6 +743,14 @@
             return Math.Floor(value * Math.Pow(10, digits)) / Math.Pow(10, digits);
         }
 
+        private static object Sec(List<Expression> p)
+        {
+            if (double.TryParse(p[0], out double number))
+                return 1.0 / Math.Cos(number);
+            else
+                throw new CellValueException();
+        }
+
         private static object SeriesSum(List<Expression> p)
         {
             var x = (Double)p[0];
diff --git a/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs b/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
index 4232028..51c4207 100644
--- a/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
+++ b/ClosedXML_Tests/Excel/CalcEngine/MathTrigTests.cs
@@ -339,6 +339,71 @@
             Assert.AreEqual(0.7, actual, tolerance);
         }
 
+        [TestCase(0, 1)]
+        [TestCase(0.3, 1.0467516)]
+        [TestCase(0.6, 1.21162831)]
+        [TestCase(0.9, 1.60872581)]
+        [TestCase(1.2, 2.759703601)]
+        [TestCase(1.5, 14.1368329)]
+        [TestCase(1.8, -4.401367872)]
+        [TestCase(2.1, -1.980801656)]
+        [TestCase(2.4, -1.356127641)]
+        [TestCase(2.7, -1.10610642)]
+        [TestCase(3.0, -1.010108666)]
+        [TestCase(3.3, -1.012678974)]
+        [TestCase(3.6, -1.115127532)]
+        [TestCase(3.9, -1.377538917)]
+        [TestCase(4.2, -2.039730601)]
+        [TestCase(4.5, -4.743927548)]
+        [TestCase(4.8, 11.42870421)]
+        [TestCase(5.1, 2.645658426)]
+        [TestCase(5.4, 1.575565187)]
+        [TestCase(5.7, 1.198016873)]
+        [TestCase(6.0, 1.041481927)]
+        [TestCase(6.3, 1.000141384)]
+        [TestCase(6.6, 1.052373922)]
+        [TestCase(6.9, 1.225903187)]
+        [TestCase(7.2, 1.643787029)]
+        [TestCase(7.5, 2.884876262)]
+        [TestCase(7.8, 18.53381902)]
+        [TestCase(8.1, -4.106031636)]
+        [TestCase(8.4, -1.925711244)]
+        [TestCase(8.7, -1.335743646)]
+        [TestCase(9.0, -1.097537906)]
+        [TestCase(9.3, -1.007835594)]
+        [TestCase(9.6, -1.015550252)]
+        [TestCase(9.9, -1.124617578)]
+        [TestCase(10.2, -1.400039323)]
+        [TestCase(10.5, -2.102886109)]
+        [TestCase(10.8, -5.145888341)]
+        [TestCase(11.1, 9.593612018)]
+        [TestCase(11.4, 2.541355049)]
+        [TestCase(45, 1.90359)]
+        [TestCase(30, 6.48292)]
+        public void Sec_ReturnsCorrectNumber(double input, double expectedOutput)
+        {
+            double result = (double)XLWorkbook.EvaluateExpr(
+                string.Format(
+                    @"SEC({0})",
+                    input.ToString(CultureInfo.InvariantCulture)));
+            Assert.AreEqual(expectedOutput, result, 0.00001);
+
+            // as the secant is symmetric for positive and negative numbers, let's assert twice:
+            double resultForNegative = (double)XLWorkbook.EvaluateExpr(
+                string.Format(
+                    @"SEC({0})",
+                    (-input).ToString(CultureInfo.InvariantCulture)));
+            Assert.AreEqual(expectedOutput, resultForNegative, 0.00001);
+        }
+
+        [Test]
+        public void Sec_ThrowsCellValueExceptionOnNonNumericValue()
+        {
+            Assert.Throws<CellValueException>(() => XLWorkbook.EvaluateExpr(
+                string.Format(
+                    @"SEC(number)")));
+        }
+
         /// <summary>
         /// refers to Example 1 from the Excel documentation,
         /// <see cref="https://support.office.com/en-us/article/SUMIF-function-169b8c99-c05c-4483-a712-1697a653039b?ui=en-US&amp;rs=en-US&amp;ad=US"/>