update comment
diff --git a/lib/openssl.c b/lib/openssl.c
index 01044a0..4e9c12e 100644
--- a/lib/openssl.c
+++ b/lib/openssl.c
@@ -859,8 +859,8 @@
ret = PTLS_ERROR_LIBRARY;
goto Exit;
}
- /* If permitted by the caller (as indicated by the opportunity to set `cancel_cb`, use the asynchronous signing method, and
- * return immediately. */
+ /* If permitted by the caller (by providing a non-NULL `async` slot), use the asynchronous signing method and return
+ * immediately. */
#ifdef PTLS_OPENSSL_HAVE_ASYNC
if (async != NULL) {
if ((*async = async_sign_ctx_new(scheme, ctx, siglen)) == NULL) {
