diff --git a/acorn.js b/acorn.js
index ede0d9e2bb..2e33050623 100644
--- a/acorn.js
+++ b/acorn.js
@@ -566,7 +566,8 @@
   // These are a run-length and offset encoded representation of the
   // >0xffff code points that are a valid part of identifiers. The
   // offset starts at 0x10000, and each pair of numbers represents an
-  // offset to the next range, and then a size of the range.
+  // offset to the next range, and then a size of the range. They were
+  // generated by tools/generate-identifier-regex.js
   var astralIdentifierStartCodes = [0,11,2,25,2,18,2,1,2,14,3,13,35,122,70,52,268,28,4,48,48,31,17,26,6,37,11,29,3,35,5,7,2,4,43,157,99,39,9,51,157,310,10,21,11,7,153,5,3,0,2,43,2,1,4,0,3,22,11,22,10,30,98,21,11,25,71,55,7,1,65,0,16,3,2,2,2,26,45,28,4,28,36,7,2,27,28,53,11,21,11,18,14,17,111,72,955,52,76,44,33,24,27,35,42,34,4,0,13,47,15,3,22,0,38,17,2,24,133,46,39,7,3,1,3,21,2,6,2,1,2,4,4,0,32,4,287,47,21,1,2,0,185,46,82,47,21,0,60,42,502,63,32,0,449,56,1288,920,104,110,2962,1070,13266,568,8,30,114,29,19,47,17,3,32,20,6,18,881,68,12,0,67,12,16481,1,3071,106,6,12,4,8,8,9,5991,84,2,70,2,1,3,0,3,1,3,3,2,11,2,0,2,6,2,64,2,3,3,7,2,6,2,27,2,3,2,4,2,0,4,6,2,339,3,24,2,24,2,30,2,24,2,30,2,24,2,30,2,24,2,30,2,24,2,7,4149,196,1340,3,2,26,2,1,2,0,3,0,2,9,2,3,2,0,2,0,7,0,5,0,2,0,2,0,2,2,2,1,2,0,3,0,2,0,2,0,2,0,2,0,2,1,2,0,3,3,2,6,2,3,2,3,2,0,2,9,2,16,6,2,2,4,2,16,4421,42710,42,4148,12,221,16355,541];
   var astralIdentifierCodes = [509,0,227,0,150,4,294,9,1368,2,2,1,6,3,41,2,5,0,166,1,1306,2,54,14,32,9,16,3,46,10,54,9,7,2,37,13,2,9,52,0,13,2,49,13,16,9,83,11,168,11,6,9,8,2,57,0,2,6,3,1,3,2,10,0,11,1,3,6,4,4,316,19,13,9,214,6,3,8,112,16,16,9,82,12,9,9,535,9,20855,9,135,4,60,6,26,9,1016,45,17,3,19723,1,5319,4,4,5,9,7,3,6,31,3,149,2,1418,49,4305,6,792618,239];
 
diff --git a/tools/generate-identifier-regex.js b/tools/generate-identifier-regex.js
index 88146e2224..0d7c50fc38 100644
--- a/tools/generate-identifier-regex.js
+++ b/tools/generate-identifier-regex.js
@@ -1,51 +1,47 @@
-// Based on https://gist.github.com/mathiasbynens/6334847 by @mathias
-
-var regenerate = require('regenerate');
+// Note: run `npm install unicode-7.0.0` first.
 
 // Which Unicode version should be used?
-var version = '7.0.0'; // note: also update `package.json` when this changes
+var version = '7.0.0';
 
-// Shorthand function
-var get = function(what) {
-    return require('unicode-' + version + '/' + what + '/code-points');
-};
+var start = require('unicode-' + version + '/properties/ID_Start/code-points')
+    .filter(function(ch) { return ch > 127; });
+var cont = [0x200c, 0x200d].concat(require('unicode-' + version + '/properties/ID_Continue/code-points')
+    .filter(function(ch) { return ch > 127 && start.indexOf(ch) == -1; }));
 
-// Unicode categories needed to construct the ES5 regex
-var Lu = get('categories/Lu');
-var Ll = get('categories/Ll');
-var Lt = get('categories/Lt');
-var Lm = get('categories/Lm');
-var Lo = get('categories/Lo');
-var Nl = get('categories/Nl');
-var Mn = get('categories/Mn');
-var Mc = get('categories/Mc');
-var Nd = get('categories/Nd');
-var Pc = get('categories/Pc');
+function pad(str, width) {
+  while (str.length < width) str = "0" + str;
+  return str;
+}
 
-var generateES5Regex = function() { // ES 5.1
-    // http://mathiasbynens.be/notes/javascript-identifiers#valid-identifier-names
-    var identifierStart = regenerate('$', '_')
-        .add(Lu, Ll, Lt, Lm, Lo, Nl)
-        .removeRange(0x010000, 0x10FFFF) // remove astral symbols
-        .removeRange(0x0, 0x7F); // remove ASCII symbols (Acorn-specific)
-    var identifierPart = regenerate('\u200C', '\u200D', Mn, Mc, Nd, Pc)
-        .removeRange(0x010000, 0x10FFFF) // remove astral symbols
-        .remove(identifierStart) // (Acorn-specific)
-        .removeRange(0x0, 0x7F); // remove ASCII symbols (Acorn-specific)
-    return {
-        'NonAsciiIdentifierStart': identifierStart.toString(),
-        'NonAsciiIdentifierPart': identifierPart.toString()
-    };
-};
+function esc(code) {
+  var hex = code.toString(16);
+  if (hex.length <= 2) return "\\x" + pad(hex, 2);
+  else return "\\u" + pad(hex, 4);
+}
 
-var result = generateES5Regex();
-console.log(
-    '// ECMAScript 5.1/Unicode v%s `nonASCIIidentifierStart`:\n\n%s\n',
-    version,
-    result.NonAsciiIdentifierStart
-);
-console.log(
-    '// ECMAScript 5.1/Unicode v%s `nonASCIIidentifier`:\n\n%s',
-    version,
-    result.NonAsciiIdentifierPart
-);
+function generate(chars) {
+  var astral = [], re = "";
+  for (var i = 0, at = 0x10000; i < chars.length; i++) {
+    var from = chars[i], to = from;
+    while (i < chars.length - 1 && chars[i + 1] == to + 1) {
+      i++;
+      to++;
+    }
+    if (to <= 0xffff) {
+      if (from == to) re += esc(from);
+      else if (from + 1 == to) re += esc(from) + esc(to);
+      else re += esc(from) + "-" + esc(to);
+    } else {
+      astral.push(from - at, to - from);
+      at = to;
+    }
+  }
+  return {nonASCII: re, astral: astral};
+}
+
+var startData = generate(start), contData = generate(cont);
+
+console.log("  var nonASCIIidentifierStartChars = \"" + startData.nonASCII + "\";");
+console.log("  var nonASCIIidentifierChars = \"" + contData.nonASCII + "\";");
+console.log("  var astralIdentifierStartCodes = " + JSON.stringify(startData.astral) + ";");
+console.log("  var astralIdentifierCodes = " + JSON.stringify(contData.astral) + ";");