diff --git a/lib/coffee_script/lexer.js b/lib/coffee_script/lexer.js
index 998f59d6..7458240e 100644
--- a/lib/coffee_script/lexer.js
+++ b/lib/coffee_script/lexer.js
@@ -1,5 +1,5 @@
 (function(){
-  var ACCESSORS, ASSIGNMENT, BEFORE_WHEN, CALLABLE, CODE, COMMENT, COMMENT_CLEANER, HEREDOC, HEREDOC_INDENT, IDENTIFIER, JS, JS_CLEANER, KEYWORDS, LAST_DENT, LAST_DENTS, MULTILINER, MULTI_DENT, NOT_REGEX, NO_NEWLINE, NUMBER, OPERATOR, REGEX, Rewriter, STRING, STRING_NEWLINES, WHITESPACE, lex;
+  var ACCESSORS, ASSIGNMENT, BEFORE_WHEN, CALLABLE, CODE, COMMENT, COMMENT_CLEANER, HEREDOC, HEREDOC_INDENT, IDENTIFIER, JS, JS_CLEANER, KEYWORDS, LAST_DENT, LAST_DENTS, MULTILINER, MULTI_DENT, NOT_REGEX, NO_NEWLINE, NUMBER, OPERATOR, REGEX, RESERVED, Rewriter, STRING, STRING_NEWLINES, WHITESPACE, lex;
   if ((typeof process !== "undefined" && process !== null)) {
     Rewriter = require('./rewriter').Rewriter;
   } else {
@@ -13,6 +13,9 @@
   // Constants ============================================================
   // The list of keywords passed verbatim to the parser.
   KEYWORDS = ["if", "else", "then", "unless", "true", "false", "yes", "no", "on", "off", "and", "or", "is", "isnt", "not", "new", "return", "try", "catch", "finally", "throw", "break", "continue", "for", "in", "of", "by", "where", "while", "delete", "instanceof", "typeof", "switch", "when", "super", "extends"];
+  // The list of keywords that are reserved by JavaScript, but not used, and aren't
+  // used by CoffeeScript. Using these will throw an error at compile time.
+  RESERVED = ["case", "default", "do", "function", "var", "void", "with", "class", "const", "let", "debugger", "enum", "export", "import", "native"];
   // Token matching regexes. (keep the IDENTIFIER regex in sync with AssignNode.)
   IDENTIFIER = /^([a-zA-Z$_](\w|\$)*)/;
   NUMBER = /^(\b((0(x|X)[0-9a-fA-F]+)|([0-9]+(\.[0-9]+)?(e[+\-]?[0-9]+)?)))\b/i;
@@ -121,6 +124,9 @@
     if (KEYWORDS.indexOf(id) >= 0 && !(ACCESSORS.indexOf(this.tag()) >= 0)) {
       tag = id.toUpperCase();
     }
+    if (RESERVED.indexOf(id) >= 0) {
+      throw new Error('SyntaxError: Reserved word "' + id + '" on line ' + this.line);
+    }
     if (tag === 'WHEN' && BEFORE_WHEN.indexOf(this.tag()) >= 0) {
       tag = 'LEADING_WHEN';
     }
diff --git a/src/lexer.coffee b/src/lexer.coffee
index 9bc3cb39..d826fba1 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -25,6 +25,13 @@ KEYWORDS: [
   "super", "extends"
 ]
 
+# The list of keywords that are reserved by JavaScript, but not used, and aren't
+# used by CoffeeScript. Using these will throw an error at compile time.
+RESERVED: [
+  "case", "default", "do", "function", "var", "void", "with", "class"
+  "const", "let", "debugger", "enum", "export", "import", "native"
+]
+
 # Token matching regexes. (keep the IDENTIFIER regex in sync with AssignNode.)
 IDENTIFIER : /^([a-zA-Z$_](\w|\$)*)/
 NUMBER     : /^(\b((0(x|X)[0-9a-fA-F]+)|([0-9]+(\.[0-9]+)?(e[+\-]?[0-9]+)?)))\b/i
@@ -110,6 +117,7 @@ lex::identifier_token: ->
       @tag(1, 'PROPERTY_ACCESS')
   tag: 'IDENTIFIER'
   tag:  id.toUpperCase() if KEYWORDS.indexOf(id) >= 0 and not (ACCESSORS.indexOf(@tag()) >= 0)
+  throw new Error('SyntaxError: Reserved word "' + id + '" on line ' + @line) if RESERVED.indexOf(id) >= 0
   tag: 'LEADING_WHEN' if tag is 'WHEN' and BEFORE_WHEN.indexOf(@tag()) >= 0
   @token(tag, id)
   @i += id.length