diff --git a/lib/compiler.js b/lib/compiler.js
index 006abbb..0fff670 100644
--- a/lib/compiler.js
+++ b/lib/compiler.js
@@ -130,7 +130,7 @@ PEG.StringUtils = {
 PEG.RegExpUtils = {
   /*
    * Escapes characters inside the string so that it can be used as a list of
-   * characters in a character class of a regular expresion.
+   * characters in a character class of a regular expression.
    */
   quoteForClass: function(s) {
     /* Based on ECMA-262, 5th ed., 7.8.5 & 15.10.1. */