Stripping static libraries

What is the safe parameters for stripping static libraries?

When I use strip command like below:

$ arm-none-linux-gnueabi-strip myCustomLib.a

it gives following error on linking:

error adding symbols: Archive has no index;
run ranlib to add one
collect2: error: ld returned 1 exit status

It is safe to use --strip-unneeded parameter which has a following short description in man page:

Remove all symbols that are not needed for relocation processing

See also: man strip