diff --git a/sbotc.c b/sbotc.c
index 06d1bc0..5ba8dc5 100644
--- a/sbotc.c
+++ b/sbotc.c
@@ -101,7 +101,7 @@ static void usage() {
 }
 
 static int auth_keypair(unsigned char *pk, unsigned char *sk, unsigned char *seed) {
-	unsigned char pk_ed[32], sk_ed[32];
+	unsigned char pk_ed[32], sk_ed[64];
 	int rc = crypto_sign_seed_keypair(pk_ed, sk_ed, seed);
 	rc |= crypto_sign_ed25519_pk_to_curve25519(pk, pk_ed);
 	rc |= crypto_sign_ed25519_sk_to_curve25519(sk, sk_ed);