Hi! With the fix for JDK-8077242 ((str) Optimize AbstractStringBuilder.append(CharSequence, int, int) for String argument) a change in behavior was introduced. In the places, where sb.append(str.substring(from, to)) used to be called, in the case of wrong indices StringIndexOutOfBoundsException was thrown. Now, after I replaced the code to sb.append(str, from, to), in such cases IndexOutOfBoundsException is thrown. The proposal is to make AbstractStringBuilder.append(CharSequence, int, int) throw more specific StringIndexOutOfBoundsException, which 1) will eliminate the regression, 2) will be more consistent with most other methods of AbstractStringBuilder, which throw StringIndexOutOfBoundsException. BUGURL: https://bugs.openjdk.java.net/browse/JDK-8130646 WEBREV: http://cr.openjdk.java.net/~igerasim/8130646/00/webrev/ Sincerely yours, Ivan