diff --git a/lib/compiler/index.js b/lib/compiler/index.js
index e1c956e..0607f8e 100644
--- a/lib/compiler/index.js
+++ b/lib/compiler/index.js
@@ -40,7 +40,7 @@ var compiler = {
    * cause its malfunction.
    */
   compile: function(ast, passes, options) {
-    options = options !== void 0 ? options : {};
+    options = options !== undefined ? options : {};
 
     var stage;
 
diff --git a/lib/compiler/passes/generate-js.js b/lib/compiler/passes/generate-js.js
index ed6aff6..4108579 100644
--- a/lib/compiler/passes/generate-js.js
+++ b/lib/compiler/passes/generate-js.js
@@ -243,7 +243,7 @@ function generateJS(ast, options) {
       '          break;',
       '',
       '        case ' + op.PUSH_UNDEFINED + ':',     // PUSH_UNDEFINED
-      '          stack.push(void 0);',
+      '          stack.push(undefined);',
       '          ip++;',
       '          break;',
       '',
@@ -430,7 +430,7 @@ function generateJS(ast, options) {
           pop: function(n) {
             var values;
 
-            if (n === void 0) {
+            if (n === undefined) {
               return s(this.sp--);
             } else {
               values = arrays.range(this.sp - n + 1, this.sp + 1).map(s);
@@ -536,7 +536,7 @@ function generateJS(ast, options) {
             break;
 
           case op.PUSH_UNDEFINED:      // PUSH_UNDEFINED
-            parts.push(stack.push('void 0'));
+            parts.push(stack.push('undefined'));
             ip++;
             break;
 
@@ -933,7 +933,7 @@ function generateJS(ast, options) {
 
     parts.push([
       'function peg$parse(input, options) {',
-      '  options = options !== void 0 ? options : {};',
+      '  options = options !== undefined ? options : {};',
       '',
       '  var peg$FAILED = {},',
       ''
@@ -1045,7 +1045,7 @@ function generateJS(ast, options) {
       '  }',
       '',
       '  function expected(description, location) {',
-      '    location = location !== void 0 ? location : peg$computeLocation(peg$savedPos, peg$currPos)',
+      '    location = location !== undefined ? location : peg$computeLocation(peg$savedPos, peg$currPos)',
       '',
       '    throw peg$buildStructuredError(',
       '      [peg$otherExpectation(description)],',
@@ -1055,7 +1055,7 @@ function generateJS(ast, options) {
       '  }',
       '',
       '  function error(message, location) {',
-      '    location = location !== void 0 ? location : peg$computeLocation(peg$savedPos, peg$currPos)',
+      '    location = location !== undefined ? location : peg$computeLocation(peg$savedPos, peg$currPos)',
       '',
       '    throw peg$buildSimpleError(message, location);',
       '  }',
diff --git a/lib/parser.js b/lib/parser.js
index 3dfcadd..cd476c6 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -130,7 +130,7 @@ peg$SyntaxError.buildMessage = function(expected, found) {
 };
 
 function peg$parse(input, options) {
-  options = options !== void 0 ? options : {};
+  options = options !== undefined ? options : {};
 
   var peg$FAILED = {},
 
@@ -514,7 +514,7 @@ function peg$parse(input, options) {
   }
 
   function expected(description, location) {
-    location = location !== void 0 ? location : peg$computeLocation(peg$savedPos, peg$currPos)
+    location = location !== undefined ? location : peg$computeLocation(peg$savedPos, peg$currPos)
 
     throw peg$buildStructuredError(
       [peg$otherExpectation(description)],
@@ -524,7 +524,7 @@ function peg$parse(input, options) {
   }
 
   function error(message, location) {
-    location = location !== void 0 ? location : peg$computeLocation(peg$savedPos, peg$currPos)
+    location = location !== undefined ? location : peg$computeLocation(peg$savedPos, peg$currPos)
 
     throw peg$buildSimpleError(message, location);
   }
@@ -1294,7 +1294,7 @@ function peg$parse(input, options) {
       }
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -1561,7 +1561,7 @@ function peg$parse(input, options) {
       }
       peg$silentFails--;
       if (s5 === peg$FAILED) {
-        s4 = void 0;
+        s4 = undefined;
       } else {
         peg$currPos = s4;
         s4 = peg$FAILED;
@@ -1593,7 +1593,7 @@ function peg$parse(input, options) {
         }
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = void 0;
+          s4 = undefined;
         } else {
           peg$currPos = s4;
           s4 = peg$FAILED;
@@ -1667,7 +1667,7 @@ function peg$parse(input, options) {
       }
       peg$silentFails--;
       if (s5 === peg$FAILED) {
-        s4 = void 0;
+        s4 = undefined;
       } else {
         peg$currPos = s4;
         s4 = peg$FAILED;
@@ -1702,7 +1702,7 @@ function peg$parse(input, options) {
         }
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = void 0;
+          s4 = undefined;
         } else {
           peg$currPos = s4;
           s4 = peg$FAILED;
@@ -1767,7 +1767,7 @@ function peg$parse(input, options) {
       s5 = peg$parseLineTerminator();
       peg$silentFails--;
       if (s5 === peg$FAILED) {
-        s4 = void 0;
+        s4 = undefined;
       } else {
         peg$currPos = s4;
         s4 = peg$FAILED;
@@ -1793,7 +1793,7 @@ function peg$parse(input, options) {
         s5 = peg$parseLineTerminator();
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = void 0;
+          s4 = undefined;
         } else {
           peg$currPos = s4;
           s4 = peg$FAILED;
@@ -1836,7 +1836,7 @@ function peg$parse(input, options) {
     s2 = peg$parseReservedWord();
     peg$silentFails--;
     if (s2 === peg$FAILED) {
-      s1 = void 0;
+      s1 = undefined;
     } else {
       peg$currPos = s1;
       s1 = peg$FAILED;
@@ -2307,7 +2307,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s2 === peg$FAILED) {
-      s1 = void 0;
+      s1 = undefined;
     } else {
       peg$currPos = s1;
       s1 = peg$FAILED;
@@ -2384,7 +2384,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s2 === peg$FAILED) {
-      s1 = void 0;
+      s1 = undefined;
     } else {
       peg$currPos = s1;
       s1 = peg$FAILED;
@@ -2584,7 +2584,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s2 === peg$FAILED) {
-      s1 = void 0;
+      s1 = undefined;
     } else {
       peg$currPos = s1;
       s1 = peg$FAILED;
@@ -2682,7 +2682,7 @@ function peg$parse(input, options) {
         s3 = peg$parseDecimalDigit();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = void 0;
+          s2 = undefined;
         } else {
           peg$currPos = s2;
           s2 = peg$FAILED;
@@ -2855,7 +2855,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s2 === peg$FAILED) {
-      s1 = void 0;
+      s1 = undefined;
     } else {
       peg$currPos = s1;
       s1 = peg$FAILED;
@@ -3130,7 +3130,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s5 === peg$FAILED) {
-      s4 = void 0;
+      s4 = undefined;
     } else {
       peg$currPos = s4;
       s4 = peg$FAILED;
@@ -3163,7 +3163,7 @@ function peg$parse(input, options) {
         }
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = void 0;
+          s4 = undefined;
         } else {
           peg$currPos = s4;
           s4 = peg$FAILED;
@@ -3235,7 +3235,7 @@ function peg$parse(input, options) {
       }
       peg$silentFails--;
       if (s5 === peg$FAILED) {
-        s4 = void 0;
+        s4 = undefined;
       } else {
         peg$currPos = s4;
         s4 = peg$FAILED;
@@ -3268,7 +3268,7 @@ function peg$parse(input, options) {
           }
           peg$silentFails--;
           if (s5 === peg$FAILED) {
-            s4 = void 0;
+            s4 = undefined;
           } else {
             peg$currPos = s4;
             s4 = peg$FAILED;
@@ -3506,7 +3506,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3543,7 +3543,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3580,7 +3580,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3617,7 +3617,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3654,7 +3654,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3691,7 +3691,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3728,7 +3728,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3765,7 +3765,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3802,7 +3802,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3839,7 +3839,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3876,7 +3876,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3913,7 +3913,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3950,7 +3950,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -3987,7 +3987,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4024,7 +4024,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4061,7 +4061,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4098,7 +4098,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4135,7 +4135,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4172,7 +4172,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4209,7 +4209,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4246,7 +4246,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4283,7 +4283,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4320,7 +4320,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4357,7 +4357,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4394,7 +4394,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4431,7 +4431,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4468,7 +4468,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4505,7 +4505,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4542,7 +4542,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4579,7 +4579,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4616,7 +4616,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4653,7 +4653,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4690,7 +4690,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4727,7 +4727,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4764,7 +4764,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4801,7 +4801,7 @@ function peg$parse(input, options) {
       s3 = peg$parseIdentifierPart();
       peg$silentFails--;
       if (s3 === peg$FAILED) {
-        s2 = void 0;
+        s2 = undefined;
       } else {
         peg$currPos = s2;
         s2 = peg$FAILED;
@@ -4950,7 +4950,7 @@ function peg$parse(input, options) {
     }
     peg$silentFails--;
     if (s1 === peg$FAILED) {
-      s0 = void 0;
+      s0 = undefined;
     } else {
       peg$currPos = s0;
       s0 = peg$FAILED;
diff --git a/lib/peg.js b/lib/peg.js
index fa2144f..ee8027c 100644
--- a/lib/peg.js
+++ b/lib/peg.js
@@ -22,7 +22,7 @@ var peg = {
    * generated parser and cause its malfunction.
    */
   generate: function(grammar, options) {
-    options = options !== void 0 ? options : {};
+    options = options !== undefined ? options : {};
 
     function convertPasses(passes) {
       var converted = {}, stage;