STRINGDECODE: MySQL function to decode unicode escapes to utf8

STRINGDECODE.sql

CREATE FUNCTION STRINGDECODE(str TEXT CHARSET utf8)
RETURNS text CHARSET utf8 DETERMINISTIC
BEGIN
declare pos         int;
declare escape      char(6) charset utf8;
declare unescape    char(3) charset utf8;
set pos = locate('\\u', str);
while pos > 0 do
    set escape = substring(str, pos, 6);
    set unescape = char(conv(substring(escape,3),16,10) using ucs2);
    set str = replace(str, escape, unescape);
    set pos = locate('\\u', str, pos+1);
end while;
return str;
END

shouldn't the second substring() at line 10 be substring(escape,3,4) ?