Parsing and reparsing disagree about automatic semicolon insertion, so that a function like function() { a = 1, } is parsed as being syntactically valid but gets a syntax error upon reparsing. This leads to an assertion failure in Parser::reparse(). It is not that big of an issue in practice, because in a release build such a function will return 'undefined' when called. Other browsers would throw a syntax error, and there aren't many people who write incorrect JS like this and only check their sites with WebKit. In this case, we are not following the spec and it should be a syntax error. However, unless there is a newline separating the ',' and the '}', JavaScriptCore would never treat it as a syntax error in the past either. It will be a bit of work to make our automatic semicolon insertion match the spec, so I am just going to match our past behaviour.