diff --git a/validator/val_secalgo.c b/validator/val_secalgo.c
index 282019632..e9ec5a5b5 100644
--- a/validator/val_secalgo.c
+++ b/validator/val_secalgo.c
@@ -1740,7 +1740,7 @@ _verify_nettle_ed25519(sldns_buffer* buf, unsigned char* sigblock,
 	}
 
 	res = ed25519_sha512_verify((uint8_t*)key, sldns_buffer_limit(buf),
-		sldns_buffer_begin(buf), sigblock);
+		sldns_buffer_begin(buf), (uint8_t*)sigblock);
 
 	if (!res)
 		return "ED25519 signature verification failed";