diff -urN coreutils-8.24/lib/vasnprintf.c coreutils-8.24-patched/lib/vasnprintf.c
--- coreutils-8.24/lib/vasnprintf.c	2015-06-16 15:04:34.000000000 +1000
+++ coreutils-8.24-patched/lib/vasnprintf.c	2019-08-28 20:59:06.000772714 +1000
@@ -849,7 +849,9 @@
   size_t a_len = a.nlimbs;
   /* 0.03345 is slightly larger than log(2)/(9*log(10)).  */
   size_t c_len = 9 * ((size_t)(a_len * (GMP_LIMB_BITS * 0.03345f)) + 1);
-  char *c_ptr = (char *) malloc (xsum (c_len, extra_zeroes));
+  /* We need extra_zeroes bytes for zeroes, followed by c_len bytes for the
+     digits of a, followed by 1 byte for the terminating NUL.  */
+  char *c_ptr = (char *) malloc (xsum (xsum (extra_zeroes, c_len), 1));
   if (c_ptr != NULL)
     {
       char *d_ptr = c_ptr;