| Index: sdk/lib/convert/ascii.dart | 
| diff --git a/sdk/lib/convert/ascii.dart b/sdk/lib/convert/ascii.dart | 
| index c8b59037711f2c08d9ada6fc4877076f8c8247d4..3f86852ac4a062a663b657abebf4de5fb11b8f26 100644 | 
| --- a/sdk/lib/convert/ascii.dart | 
| +++ b/sdk/lib/convert/ascii.dart | 
| @@ -290,7 +290,8 @@ class _SimpleAsciiDecoderSink extends ByteConversionSinkBase { | 
| void add(List<int> source) { | 
| for (int i = 0; i < source.length; i++) { | 
| if ((source[i] & ~_ASCII_MASK) != 0) { | 
| -        throw new FormatException("Source contains non-ASCII bytes."); | 
| +        throw new FormatException("Source contains non-ASCII bytes.", | 
| +                                  source, i); | 
| } | 
| } | 
| _sink.add(new String.fromCharCodes(source)); | 
|  |