Comparison between signed and unsigned integer expressions in http.c on ARM7

I get the following warning when building main on 32-bit ARM7 with GCC 6.3.0:

netmgr/http.c: In function ‘https_readcb’:
netmgr/http.c:707:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (readlen < region->length) {
              ^