diff --git a/tommath.h b/tommath.h
index 0097b5e..1391d95 100644
--- a/tommath.h
+++ b/tommath.h
@@ -504,7 +504,7 @@ int mp_exptmod(mp_int *a, mp_int *b, mp_int *c, mp_int *d);
 #endif
 
 /* table of first PRIME_SIZE primes */
-extern const mp_digit ltm_prime_tab[];
+extern const mp_digit ltm_prime_tab[PRIME_SIZE];
 
 /* result=1 if a is divisible by one of the first PRIME_SIZE primes */
 int mp_prime_is_divisible(mp_int *a, int *result);