diff --git a/lib/querystring.js b/lib/querystring.js
index b3b6b84c76632f..e0666a45baeefa 100644
--- a/lib/querystring.js
+++ b/lib/querystring.js
@@ -6,29 +6,25 @@ const QueryString = exports;
 const Buffer = require('buffer').Buffer;
 
 
-function charCode(c) {
-  return c.charCodeAt(0);
-}
-
-
 // a safe fast alternative to decodeURIComponent
 QueryString.unescapeBuffer = function(s, decodeSpaces) {
   var out = new Buffer(s.length);
-  var state = 'CHAR'; // states: CHAR, HEX0, HEX1
+  var state = 0;
   var n, m, hexchar;
 
   for (var inIndex = 0, outIndex = 0; inIndex <= s.length; inIndex++) {
-    var c = s.charCodeAt(inIndex);
+    var c = inIndex < s.length ? s.charCodeAt(inIndex) : NaN;
     switch (state) {
-      case 'CHAR':
+      case 0: // Any character
         switch (c) {
-          case charCode('%'):
+          case 37: // '%'
             n = 0;
             m = 0;
-            state = 'HEX0';
+            state = 1;
             break;
-          case charCode('+'):
-            if (decodeSpaces) c = charCode(' ');
+          case 43: // '+'
+            if (decodeSpaces)
+              c = 32; // ' '
             // falls through
           default:
             out[outIndex++] = c;
@@ -36,33 +32,33 @@ QueryString.unescapeBuffer = function(s, decodeSpaces) {
         }
         break;
 
-      case 'HEX0':
-        state = 'HEX1';
+      case 1: // First hex digit
         hexchar = c;
-        if (charCode('0') <= c && c <= charCode('9')) {
-          n = c - charCode('0');
-        } else if (charCode('a') <= c && c <= charCode('f')) {
-          n = c - charCode('a') + 10;
-        } else if (charCode('A') <= c && c <= charCode('F')) {
-          n = c - charCode('A') + 10;
+        if (c >= 48/*0*/ && c <= 57/*9*/) {
+          n = c - 48/*0*/;
+        } else if (c >= 65/*A*/ && c <= 70/*F*/) {
+          n = c - 65/*A*/ + 10;
+        } else if (c >= 97/*a*/ && c <= 102/*f*/) {
+          n = c - 97/*a*/ + 10;
         } else {
-          out[outIndex++] = charCode('%');
+          out[outIndex++] = 37/*%*/;
           out[outIndex++] = c;
-          state = 'CHAR';
+          state = 0;
           break;
         }
+        state = 2;
         break;
 
-      case 'HEX1':
-        state = 'CHAR';
-        if (charCode('0') <= c && c <= charCode('9')) {
-          m = c - charCode('0');
-        } else if (charCode('a') <= c && c <= charCode('f')) {
-          m = c - charCode('a') + 10;
-        } else if (charCode('A') <= c && c <= charCode('F')) {
-          m = c - charCode('A') + 10;
+      case 2: // Second hex digit
+        state = 0;
+        if (c >= 48/*0*/ && c <= 57/*9*/) {
+          m = c -  48/*0*/;
+        } else if (c >= 65/*A*/ && c <= 70/*F*/) {
+          m = c - 65/*A*/ + 10;
+        } else if (c >= 97/*a*/ && c <= 102/*f*/) {
+          m = c - 97/*a*/ + 10;
         } else {
-          out[outIndex++] = charCode('%');
+          out[outIndex++] = 37/*%*/;
           out[outIndex++] = hexchar;
           out[outIndex++] = c;
           break;