diff --git a/libfreefare/freefare_internal.h b/libfreefare/freefare_internal.h
index e26c3cb..f4c9023 100644
--- a/libfreefare/freefare_internal.h
+++ b/libfreefare/freefare_internal.h
@@ -243,7 +243,7 @@ struct mifare_desfire_tag {
     uint32_t selected_application;
 };
 
-MifareDESFireKey mifare_desfire_session_key_new (uint8_t rnda[8], uint8_t rndb[8], MifareDESFireKey authentication_key);
+MifareDESFireKey mifare_desfire_session_key_new (uint8_t rnda[], uint8_t rndb[], MifareDESFireKey authentication_key);
 const char	*mifare_desfire_error_lookup (uint8_t error);
 
 struct mifare_ultralight_tag {
diff --git a/libfreefare/mifare_desfire_key.c b/libfreefare/mifare_desfire_key.c
index efa63c1..ebf18c9 100644
--- a/libfreefare/mifare_desfire_key.c
+++ b/libfreefare/mifare_desfire_key.c
@@ -158,7 +158,7 @@ mifare_desfire_key_set_version (MifareDESFireKey key, uint8_t version)
 }
 
 MifareDESFireKey
-mifare_desfire_session_key_new (uint8_t rnda[8], uint8_t rndb[8], MifareDESFireKey authentication_key)
+mifare_desfire_session_key_new (uint8_t rnda[], uint8_t rndb[], MifareDESFireKey authentication_key)
 {
     MifareDESFireKey key = NULL;