diff --git a/src/crypto.c b/src/crypto.c
index 475ebf36..cd50d6f7 100644
--- a/src/crypto.c
+++ b/src/crypto.c
@@ -389,7 +389,9 @@ bool aes_siv_decrypt(const void *key, size_t key_len, const void *in,
 	if (in_len < 16)
 		return false;
 
-	memcpy(iov, ad, sizeof(struct iovec) * num_ad);
+	if (ad)
+		memcpy(iov, ad, sizeof(struct iovec) * num_ad);
+
 	iov[num_ad].iov_base = (void *)out;
 	iov[num_ad].iov_len = in_len - 16;
 	num_ad++;