diff --git a/Jakefile b/Jakefile
index 5bc5a1d..7231a7e 100644
--- a/Jakefile
+++ b/Jakefile
@@ -1,4 +1,4 @@
-var sys          = require("sys");
+var util         = require("util");
 var fs           = require("fs");
 var path         = require("path");
 var childProcess = require("child_process");
@@ -53,7 +53,7 @@ function exitFailure() {
 }
 
 function abort(message) {
-  sys.error(message);
+  util.error(message);
   exitFailure();
 }
 
diff --git a/benchmark/run b/benchmark/run
index c51e8b3..254915c 100755
--- a/benchmark/run
+++ b/benchmark/run
@@ -1,8 +1,8 @@
 #!/usr/bin/env node
 
-var sys = require("sys");
-var fs  = require("fs");
-var PEG = require("../lib/peg");
+var util = require("util");
+var fs   = require("fs");
+var PEG  = require("../lib/peg");
 
 [
   "benchmarks.js",
@@ -37,21 +37,21 @@ function center(text, length) {
 }
 
 function writeTableHeader() {
-  sys.puts("┌─────────────────────────────────────┬───────────┬────────────┬──────────────┐");
-  sys.puts("│                Test                 │ Inp. size │ Avg. time  │  Avg. speed  │");
+  util.puts("┌─────────────────────────────────────┬───────────┬────────────┬──────────────┐");
+  util.puts("│                Test                 │ Inp. size │ Avg. time  │  Avg. speed  │");
 }
 
 function writeHeading(heading) {
-  sys.puts("├─────────────────────────────────────┴───────────┴────────────┴──────────────┤");
-  sys.puts("│ " + center(heading, 75) + " │");
-  sys.puts("├─────────────────────────────────────┬───────────┬────────────┬──────────────┤");
+  util.puts("├─────────────────────────────────────┴───────────┴────────────┴──────────────┤");
+  util.puts("│ " + center(heading, 75) + " │");
+  util.puts("├─────────────────────────────────────┬───────────┬────────────┬──────────────┤");
 }
 
 function writeResult(title, inputSize, parseTime) {
   var KB      = 1024;
   var MS_IN_S = 1000;
 
-  sys.puts("│ "
+  util.puts("│ "
     + padRight(title, 35)
     + " │ "
     + padLeft((inputSize / KB).toFixed(2), 6)
@@ -64,11 +64,11 @@ function writeResult(title, inputSize, parseTime) {
 }
 
 function writeSeparator() {
-  sys.puts("├─────────────────────────────────────┼───────────┼────────────┼──────────────┤");
+  util.puts("├─────────────────────────────────────┼───────────┼────────────┼──────────────┤");
 }
 
 function writeTableFooter() {
-  sys.puts("└─────────────────────────────────────┴───────────┴────────────┴──────────────┘");
+  util.puts("└─────────────────────────────────────┴───────────┴────────────┴──────────────┘");
 }
 
 /* Helpers */
@@ -78,7 +78,7 @@ function exitFailure() {
 }
 
 function abort(message) {
-  sys.error(message);
+  util.error(message);
   exitFailure();
 }
 
@@ -100,8 +100,8 @@ switch (args.length) {
     abort("Too many arguments.");
 }
 
-sys.puts("Each test is run " + runCount + " times.");
-sys.puts("");
+util.puts("Each test is run " + runCount + " times.");
+util.puts("");
 
 Runner.run(benchmarks, runCount, {
   readFile: function(file) {
diff --git a/bin/pegjs b/bin/pegjs
index 46694e5..08ca376 100755
--- a/bin/pegjs
+++ b/bin/pegjs
@@ -1,30 +1,30 @@
 #!/usr/bin/env node
 
-var sys = require("sys");
-var fs  = require("fs");
-var PEG = require("../lib/peg");
+var util = require("util");
+var fs   = require("fs");
+var PEG  = require("../lib/peg");
 
 /* Helpers */
 
 function printVersion() {
-  sys.puts("PEG.js " + PEG.VERSION);
+  util.puts("PEG.js " + PEG.VERSION);
 }
 
 function printHelp() {
-  sys.puts("Usage: pegjs [options] [--] [<input_file>] [<output_file>]");
-  sys.puts("");
-  sys.puts("Generates a parser from the PEG grammar specified in the <input_file> and");
-  sys.puts("writes it to the <output_file>.");
-  sys.puts("");
-  sys.puts("If the <output_file> is omitted, its name is generated by changing the");
-  sys.puts("<input_file> extension to \".js\". If both <input_file> and <output_file> are");
-  sys.puts("omitted, standard input and output are used.");
-  sys.puts("");
-  sys.puts("Options:");
-  sys.puts("  -e, --export-var <variable>  name of the variable where the parser object");
-  sys.puts("                               will be stored (default: \"module.exports\")");
-  sys.puts("  -v, --version                print version information and exit");
-  sys.puts("  -h, --help                   print help and exit");
+  util.puts("Usage: pegjs [options] [--] [<input_file>] [<output_file>]");
+  util.puts("");
+  util.puts("Generates a parser from the PEG grammar specified in the <input_file> and");
+  util.puts("writes it to the <output_file>.");
+  util.puts("");
+  util.puts("If the <output_file> is omitted, its name is generated by changing the");
+  util.puts("<input_file> extension to \".js\". If both <input_file> and <output_file> are");
+  util.puts("omitted, standard input and output are used.");
+  util.puts("");
+  util.puts("Options:");
+  util.puts("  -e, --export-var <variable>  name of the variable where the parser object");
+  util.puts("                               will be stored (default: \"module.exports\")");
+  util.puts("  -v, --version                print version information and exit");
+  util.puts("  -h, --help                   print help and exit");
 }
 
 function exitSuccess() {
@@ -36,7 +36,7 @@ function exitFailure() {
 }
 
 function abort(message) {
-  sys.error(message);
+  util.error(message);
   exitFailure();
 }
 
diff --git a/test/run b/test/run
index 551aa3c..98192a8 100755
--- a/test/run
+++ b/test/run
@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 
-var sys   = require("sys");
+var util  = require("util");
 var fs    = require("fs");
 var PEG   = require("../lib/peg");
 var QUnit = require("./vendor/qunit/qunit").QUnit;
@@ -19,8 +19,8 @@ QUnit.config.blocking = true;
 QUnit.config.updateRate = 0;
 
 QUnit.moduleStart = function(details) {
-  sys.puts("");
-  sys.puts(bold(details.name));
+  util.puts("");
+  util.puts(bold(details.name));
 };
 
 var failedAssertions = [];
@@ -31,12 +31,12 @@ QUnit.testStart = function(details) {
 
 QUnit.testDone = function(details) {
   if (details.failed == 0) {
-    sys.puts('✔ ' + details.name);
+    util.puts('✔ ' + details.name);
   } else {
-    sys.puts(error('✖ ' + details.name));
-    sys.puts("");
+    util.puts(error('✖ ' + details.name));
+    util.puts("");
     failedAssertions.forEach(function(assertion) {
-      sys.puts(assertion);
+      util.puts(assertion);
     });
   }
 };
@@ -59,15 +59,15 @@ QUnit.log = function(details) {
 };
 
 QUnit.done = function(details) {
-  sys.puts("");
+  util.puts("");
   if (details.failed > 0) {
-    sys.puts(bold(error("FAILURES: "))
+    util.puts(bold(error("FAILURES: "))
       + details.failed + "/"
       + details.total + " assertions failed ("
       + details.runtime + " ms)"
     );
   } else {
-    sys.puts(bold(ok('OK: '))
+    util.puts(bold(ok('OK: '))
       + details.total + " assertions ("
       + details.runtime + " ms)"
     )