diff --git a/lib/network/dotparser.js b/lib/network/dotparser.js
index 758c3131fc..90c7417ce3 100644
--- a/lib/network/dotparser.js
+++ b/lib/network/dotparser.js
@@ -115,15 +115,37 @@ function nextPreview() {
   return dot.charAt(index + 1);
 }
 
-var regexAlphaNumeric = /[a-zA-Z_0-9.:#]/;
 /**
- * Test whether given character is alphabetic or numeric
+ * Test whether given character is alphabetic or numeric ( a-zA-Z_0-9.:# )
  *
  * @param {string} c
  * @returns {boolean} isAlphaNumeric
  */
 function isAlphaNumeric(c) {
-  return regexAlphaNumeric.test(c);
+  var charCode = c.charCodeAt(0);
+
+  if (charCode < 47) {
+    // #.
+    return charCode === 35 || charCode === 46;
+  }
+  if (charCode < 59) {
+    // 0-9 and :
+    return charCode > 47;
+  }
+  if (charCode < 91) {
+    // A-Z
+    return charCode > 64;
+  }
+  if (charCode < 96) {
+    // _
+    return charCode === 95;
+  }
+  if (charCode < 123) {
+    // a-z
+    return charCode > 96;
+  }
+
+  return false;
 }
 
 /**