The following program: http://play.golang.org/p/Xz1-Us2Cwl is rejected with:
/tmp/sandbox748824652/main.go:4: constant -48 overflows uint8

However, indexing a string constant with a constant index does not produce a constant, and thus the program should be valid.

See also #11368.