diff --git a/ClosedXML/ClosedXML/ClosedXML/ExcelHelper.cs b/ClosedXML/ClosedXML/ClosedXML/ExcelHelper.cs
index 9b85972..225f52e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/ExcelHelper.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/ExcelHelper.cs
@@ -126,7 +126,7 @@
             if (length == 2)
                 return isValid && theColumn[1] >= 'A' && theColumn[1] <= 'Z';
 
-            if (theColumn[0] < 'X')
+            if (theColumn[0] >= 'A' && theColumn[0] < 'X')
                 return theColumn[1] >= 'A' && theColumn[1] <= 'Z'
                        && theColumn[2] >= 'A' && theColumn[2] <= 'Z';
 
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Misc/ExcelHelperTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Misc/ExcelHelperTests.cs
index fba3eaa..a675463 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Misc/ExcelHelperTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Misc/ExcelHelperTests.cs
@@ -28,6 +28,72 @@
         {
             Assert.AreEqual(column, XLHelper.GetColumnNumberFromLetter(XLHelper.GetColumnLetterFromNumber(column)));
         }
-        
+
+        [TestMethod]
+        public void PlusAA1_Is_Not_an_address()
+        {
+            Assert.IsFalse(XLHelper.IsValidA1Address("+AA1"));
+        }
+
+        [TestMethod]
+        public void ValidA1Addresses()
+        {
+            Assert.IsTrue(XLHelper.IsValidA1Address("A1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address("A" + XLHelper.MaxRowNumber ));
+            Assert.IsTrue(XLHelper.IsValidA1Address("Z1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address("Z" + XLHelper.MaxRowNumber));
+
+            Assert.IsTrue(XLHelper.IsValidA1Address("AA1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address("AA" + XLHelper.MaxRowNumber));
+            Assert.IsTrue(XLHelper.IsValidA1Address("ZZ1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address("ZZ" + XLHelper.MaxRowNumber));
+
+            Assert.IsTrue(XLHelper.IsValidA1Address("AAA1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address("AAA" + XLHelper.MaxRowNumber));
+            Assert.IsTrue(XLHelper.IsValidA1Address(XLHelper.MaxColumnLetter + "1"));
+            Assert.IsTrue(XLHelper.IsValidA1Address(XLHelper.MaxColumnLetter + XLHelper.MaxRowNumber));
+        }
+
+        [TestMethod]
+        public void InvalidA1Addresses()
+        {
+            Assert.IsFalse(XLHelper.IsValidA1Address(""));
+            Assert.IsFalse(XLHelper.IsValidA1Address("A"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("a"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("-1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AAAA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("XFG1"));
+
+            Assert.IsFalse(XLHelper.IsValidA1Address("@A1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("@AA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("@AAA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[A1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[AA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[AAA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{A1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{AA1"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{AAA1"));
+
+            Assert.IsFalse(XLHelper.IsValidA1Address("A1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AA1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AAA1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("A1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AA1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AAA1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("A1{"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AA1{"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("AAA1{"));
+
+            Assert.IsFalse(XLHelper.IsValidA1Address("@A1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("@AA1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("@AAA1@"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[A1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[AA1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("[AAA1["));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{A1{"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{AA1{"));
+            Assert.IsFalse(XLHelper.IsValidA1Address("{AAA1{"));
+        }
     }
 }