That's the grammar for PHP integer literals[1]: decimal : [1-9][0-9]* | 0 hexadecimal : 0[xX][0-9a-fA-F]+ octal

That's the grammar for PHP integer literals[1]: decimal : [1-9][0-9]* | 0 hexadecimal : 0[xX][0-9a-fA-F]+ octal : 0[0-7]+ integer : [+-]?decimal | [+-]?hexadecimal | [+-]?octal "08" and "09" do not match any of these. php -r "var_dump(08);" Yields "int(0)", while the case should rather be treated as a syntax error, if you ask me. The bottom line probably is that your literals just shouldn't have leading zeroes… [1] http://www.php.net/manual/en/language.types.integer.php http://www.php.net/manual/en/language.types.integer.php