diff --git a/lib/sfrsd2/sfrsd_paper/binomial_subs.c b/lib/sfrsd2/sfrsd_paper/binomial_subs.c
index 32b9e94ae..139488b2f 100644
--- a/lib/sfrsd2/sfrsd_paper/binomial_subs.c
+++ b/lib/sfrsd2/sfrsd_paper/binomial_subs.c
@@ -7,8 +7,8 @@
  
 /* We go to some effort to handle overflow situations */
  
-static unsigned long gcd_ui(unsigned long x, unsigned long y) {
-  unsigned long t;
+static unsigned long long gcd_ui(unsigned long long x, unsigned long long y) {
+  unsigned long long t;
   if (y < x) { t = x; x = y; y = t; }
   while (y > 0) {
     t = y;  y = x % y;  x = t;  /* y1 <- x0 % y0 ; x1 <- y0 */
@@ -16,18 +16,18 @@ static unsigned long gcd_ui(unsigned long x, unsigned long y) {
   return x;
 }
  
-unsigned long binomial(unsigned long n, unsigned long k) {
-  unsigned long d, g, r = 1;
+unsigned long long binomial(unsigned long long n, unsigned long long k) {
+  unsigned long long d, g, r = 1;
   if (k == 0) return 1;
   if (k == 1) return n;
   if (k >= n) return (k == n);
   if (k > n/2) k = n-k;
   for (d = 1; d <= k; d++) {
-    if (r >= ULONG_MAX/n) {  /* Possible overflow */
-      unsigned long nr, dr;  /* reduced numerator / denominator */
+    if (r >= ULONG_LONG_MAX/n) {  /* Possible overflow */
+      unsigned long long nr, dr;  /* reduced numerator / denominator */
       g = gcd_ui(n, d);  nr = n/g;  dr = d/g;
       g = gcd_ui(r, dr);  r = r/g;  dr = dr/g;
-      if (r >= ULONG_MAX/nr) return 0;  /* Unavoidable overflow */
+      if (r >= ULONG_LONG_MAX/nr) return 0;  /* Unavoidable overflow */
       r *= nr;
       r /= dr;
       n--;
@@ -39,7 +39,7 @@ unsigned long binomial(unsigned long n, unsigned long k) {
   return r;
 }
 
-unsigned long binomial_(int *n, int *k)
+unsigned long long binomial_(int *n, int *k)
 {
   //  printf("n=%d  k=%d  %lu\n",*n,*k,binomial(*n,*k));
   return binomial(*n,*k);