diff --git a/src/make-prime-list.c b/src/make-prime-list.c
index 4ec01cf..d293e50 100644
--- a/src/make-prime-list.c
+++ b/src/make-prime-list.c
@@ -195,8 +195,8 @@ main (int argc, char **argv)
 
   size = (limit-1)/2;
   /* sieve[i] represents 3+2*i */
-  sieve = xalloc (size);
-  memset (sieve, 1, size);
+  sieve = xalloc (size+1);
+  memset (sieve, 1, size+1);
 
   prime_list = xalloc (size * sizeof (*prime_list));
   nprimes = 0;