diff --git a/ClosedXML/ClosedXML/ClosedXML/Extensions.cs b/ClosedXML/ClosedXML/ClosedXML/Extensions.cs
index 8443b32..212b26c 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Extensions.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Extensions.cs
@@ -59,8 +59,7 @@
             StringBuilder sb = new StringBuilder();
             foreach (char c in str)
             {
-                //if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') | c == '.' || c == '_')
-                if (Char.IsLetterOrDigit(c))
+                if (Char.IsLetterOrDigit(c) || c == '.' || c == '_')
                 {
                     sb.Append(c);
                 }