diff --git a/ClosedXML_Tests/Excel/Misc/XlHelperTests.cs b/ClosedXML_Tests/Excel/Misc/XlHelperTests.cs
index 20853d6..7ef97ff 100644
--- a/ClosedXML_Tests/Excel/Misc/XlHelperTests.cs
+++ b/ClosedXML_Tests/Excel/Misc/XlHelperTests.cs
@@ -1,5 +1,7 @@
 using ClosedXML.Excel;
 using NUnit.Framework;
+using System;
+using System.Collections.Generic;
 
 namespace ClosedXML_Tests.Excel
 {
@@ -71,6 +73,7 @@
             CheckColumnNumber(52);
             CheckColumnNumber(53);
             CheckColumnNumber(1000);
+            CheckColumnNumber(1353);
         }
 
         [Test]
@@ -91,5 +94,81 @@
             Assert.IsTrue(XLHelper.IsValidA1Address(XLHelper.MaxColumnLetter + "1"));
             Assert.IsTrue(XLHelper.IsValidA1Address(XLHelper.MaxColumnLetter + XLHelper.MaxRowNumber));
         }
+
+        [Test]
+        public void TestColumnLetterLookup()
+        {
+            var columnLetters = new List<String>();
+            for (int c = 1; c <= XLHelper.MaxColumnNumber; c++)
+            {
+                var columnLetter = NaiveGetColumnLetterFromNumber(c);
+                columnLetters.Add(columnLetter);
+
+                Assert.AreEqual(columnLetter, XLHelper.GetColumnLetterFromNumber(c));
+            }
+
+            foreach (var cl in columnLetters)
+            {
+                var columnNumber = NaiveGetColumnNumberFromLetter(cl);
+                Assert.AreEqual(columnNumber, XLHelper.GetColumnNumberFromLetter(cl));
+            }
+        }
+
+        #region Old XLHelper methods
+
+        private static readonly string[] letters = new[] { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };
+
+        /// <summary>
+        /// These used to be the methods in XLHelper, but were later changed
+        /// We now use them as a check against the new methods
+        /// Gets the column number of a given column letter.
+        /// </summary>
+        /// <param name="columnLetter"> The column letter to translate into a column number. </param>
+        private static int NaiveGetColumnNumberFromLetter(string columnLetter)
+        {
+            if (string.IsNullOrEmpty(columnLetter)) throw new ArgumentNullException("columnLetter");
+
+            int retVal;
+            columnLetter = columnLetter.ToUpper();
+
+            //Extra check because we allow users to pass row col positions in as strings
+            if (columnLetter[0] <= '9')
+            {
+                retVal = Int32.Parse(columnLetter, XLHelper.NumberStyle, XLHelper.ParseCulture);
+                return retVal;
+            }
+
+            int sum = 0;
+
+            for (int i = 0; i < columnLetter.Length; i++)
+            {
+                sum *= 26;
+                sum += (columnLetter[i] - 'A' + 1);
+            }
+
+            return sum;
+        }
+
+        /// <summary>
+        /// Gets the column letter of a given column number.
+        /// </summary>
+        /// <param name="columnNumber">The column number to translate into a column letter.</param>
+        /// <param name="trimToAllowed">if set to <c>true</c> the column letter will be restricted to the allowed range.</param>
+        /// <returns></returns>
+        private static string NaiveGetColumnLetterFromNumber(int columnNumber, bool trimToAllowed = false)
+        {
+            if (trimToAllowed) columnNumber = XLHelper.TrimColumnNumber(columnNumber);
+
+            columnNumber--; // Adjust for start on column 1
+            if (columnNumber <= 25)
+            {
+                return letters[columnNumber];
+            }
+            var firstPart = (columnNumber) / 26;
+            var remainder = ((columnNumber) % 26) + 1;
+            return NaiveGetColumnLetterFromNumber(firstPart) + NaiveGetColumnLetterFromNumber(remainder);
+        }
+
+        #endregion Old XLHelper methods
     }
-}
\ No newline at end of file
+}