PVS-Studio warning V579 for peerblock

void Curl_strntoupper(char *dest, const char *src, size_t n)
{
  if(n < 1)
    return;

  do {
    *dest++ = Curl_raw_toupper(*src);
  } while(*src++ && --n);
}

CURLcode Curl_rtsp_parseheader(....)
{
  ...
  char *temp = strdup(header);
  ...
  Curl_strntoupper(temp, temp, sizeof(temp));
  ...
}

This suspicious code was found in peerblock project by PVS-Studio static code analyzer.
Warning message is:
V579 The Curl_strntoupper function receives the pointer and its size as arguments. It is possibly a mistake. Inspect the third argument. libcurl rtsp.c 753

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/