I want to use json-parser on pebble, but I get compilation error:

json.c:49:4: error: array subscript has type 'char' [-Werror=char-subscripts]

Following comments on http://stackoverflow.com/questions/10186219/array-subscript-has-type-char I needed to cast the parameter on (unsigned char):

   if (isdigit((unsigned char)c))
      return c - '0';

I needed to repeat it in four places.

Is there any other solution?