diff --git a/ClosedXML/XLHelper.cs b/ClosedXML/XLHelper.cs
index a5983ec..b2bafb8 100644
--- a/ClosedXML/XLHelper.cs
+++ b/ClosedXML/XLHelper.cs
@@ -25,7 +25,7 @@
         internal static readonly NumberFormatInfo NumberFormatForParse = CultureInfo.InvariantCulture.NumberFormat;
         internal static readonly Graphics Graphic = Graphics.FromImage(new Bitmap(200, 200));
         internal static readonly Double DpiX = Graphic.DpiX;
-        internal static readonly NumberStyles NumberStyle = NumberStyles.AllowDecimalPoint;
+        internal static readonly NumberStyles NumberStyle = NumberStyles.AllowDecimalPoint | NumberStyles.AllowLeadingSign | NumberStyles.AllowLeadingWhite | NumberStyles.AllowTrailingWhite;
         internal static readonly CultureInfo ParseCulture = CultureInfo.InvariantCulture;
 
         internal static readonly Regex A1SimpleRegex = new Regex(