1 files changed, 1 insertions, 1 deletions

diff --git a/src/es256.c b/src/es256.c
index 020ecaa..5b4e6d6 100644
--- a/src/es256.c
+++ b/src/es256.c
@@ -92,7 +92,7 @@ es256_pk_encode(const es256_pk_t *pk, int ecdh)
 
         /* alg */
         if ((argv[1].key = cbor_build_uint8(3)) == NULL ||
-            (argv[1].value = cbor_build_negint8(-alg - 1)) == NULL ||
+            (argv[1].value = cbor_build_negint8((uint8_t)(-alg - 1))) == NULL ||
             !cbor_map_add(item, argv[1]))
                 goto fail;