diff --git a/crypto.c b/crypto.c
index b4f71e4..31ba396 100644
--- a/crypto.c
+++ b/crypto.c
@@ -203,7 +203,8 @@ brandt_mpi_scan_unsigned (gcry_mpi_t *result, const void *data, size_t size)
 /**
  * brandt_ec_skey_create
  *
- * @param[out] skey where to store the generated secret key
+ * @param[out] skey where to store the generated secret key. This has to be an
+ * already initialized mpi.
  */
 void
 brandt_ec_skey_create (gcry_mpi_t skey)