diff --git a/src/modules/Gmp/next_prime.c b/src/modules/Gmp/next_prime.c
index ba47d9c47e18437b4591bc6aae29b809da128ed1..9a4de5da14c686061514a72fc4f23d802f8abc53 100644
--- a/src/modules/Gmp/next_prime.c
+++ b/src/modules/Gmp/next_prime.c
@@ -138,7 +138,7 @@ void
 mpz_next_prime(mpz_t p, mpz_t n, int count, int prime_limit)
 {
   mpz_t tmp;
-  unsigned long *moduli = NULL;
+  unsigned long *moduli = 0;
   unsigned long difference;
   int i;
   int composite;