Version-Release number of selected component (if applicable):
glibc-2.3.2-101.4

Steps to Reproduce:
#include <limits.h>
#include <locale.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>

int
main (void)
{
  wchar_t wc;

  setlocale (LC_CTYPE, "en_US.UTF-8");
  printf ("%d\n", mbtowc (&wc, "\xc3\xa1", MB_LEN_MAX));
  printf ("%d\n", mbtowc (&wc, "\xc3\xa1", SIZE_MAX));
  return EXIT_SUCCESS;
}

  
Actual results:
2
-1

Expected results:
2
2