diff --git a/src/bn/relic_bn_rec.c b/src/bn/relic_bn_rec.c
index 323b363bc..d61cb9715 100644
--- a/src/bn/relic_bn_rec.c
+++ b/src/bn/relic_bn_rec.c
@@ -895,16 +895,16 @@ void bn_rec_sac(int8_t *b, size_t *len, bn_t *k, size_t c, size_t m, size_t n) {
 	}
 
 	RLC_TRY {
+		/* The current basis for some curves might be one bit longer. */
+		fp_prime_get_par(t[0]);
+		l = RLC_MAX(l, bn_bits(t[0]) + 1);
 		for (size_t i = 0; i < m; i++) {
 			bn_null(t[i]);
 			bn_new(t[i]);
 			bn_copy(t[i], k[i]);
 		}
 
-		/* The current basis for BN curves might be one bit longer. */
-		for (size_t i = 0; i < m; i++) {
-			l = RLC_MAX(l, bn_bits(k[i]) + 1);
-		}
+		memset(b, 0, *len);
 
 		b[l - 1] = 0;
 		for (size_t i = 0; i < l - 1; i++) {