Error message of pointer of type `void *' used in arithmetic in g++

[Crap]

Hi there

there is this little part of my project that has a few lines involving 
moving a void pointer to and fro by a few bytes, i.e.  ptr += (something) 
or ptr -= (something) where ptr is of type void *

The code compiles fine in gcc and the program works perfect with no memory 
leaks or seg faults, but this won't compile with g++ at all and it keeps 
complaining with error messages of :

         pointer of type `void *' used in arithmetic

on those lines with ath void pointer that I have mentioned.  Is there some 
flag in g++ to get rid of this annoying issue? I have gcc/g++ 3.2.2

Thanks