--- old/src/share/vm/opto/stringopts.cpp	2015-11-05 13:06:24.141214874 +0100
+++ new/src/share/vm/opto/stringopts.cpp	2015-11-05 13:06:24.073214876 +0100
@@ -1520,7 +1520,7 @@
       Node* adr = kit.array_element_address(dst_array, index, T_BYTE);
       jchar val;
       if (src_is_byte) {
-        val = src_array->byte_at(i);
+        val = src_array->byte_at(i) & 0xff;
       } else {
         val = readChar(src_array, i++);
       }