diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
index 8758174..f43aa6a 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
@@ -8,6 +8,13 @@
     [TestFixture]
     public class FunctionsTests
     {
+        [TestFixtureSetUp]
+        public void Init()
+        {
+            // Make sure tests run on a deterministic culture
+            System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-US");
+        }
+
         [Test]
         public void Asc()
         {
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/TestHelper.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/TestHelper.cs
index 35fde24..d0cdbf0 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/TestHelper.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/TestHelper.cs
@@ -44,6 +44,9 @@
         public static void RunTestExample<T>(string filePartName)
                 where T : IXLExample, new()
         {
+            // Make sure tests run on a deterministic culture
+            Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-US");
+
             var example = new T();
             string filePath1 = Path.Combine(TestsExampleOutputDirectory, filePartName);