we do not need this
diff --git a/lib/openssl.c b/lib/openssl.c
index 4e9c12e..0553ad1 100644
--- a/lib/openssl.c
+++ b/lib/openssl.c
@@ -93,8 +93,6 @@
 
 #endif
 
-struct async_sign_ctx;
-
 static const struct st_ptls_openssl_signature_scheme_t rsa_signature_schemes[] = {{PTLS_SIGNATURE_RSA_PSS_RSAE_SHA256, EVP_sha256},
                                                                                   {PTLS_SIGNATURE_RSA_PSS_RSAE_SHA384, EVP_sha384},
                                                                                   {PTLS_SIGNATURE_RSA_PSS_RSAE_SHA512, EVP_sha512},