diff --git a/src/tls/openssl.c b/src/tls/openssl.c
index 14b77e09c6a..03aeb9610b7 100644
--- a/src/tls/openssl.c
+++ b/src/tls/openssl.c
@@ -217,7 +217,7 @@ static int tls_context_server_alpn_select_callback(SSL *ssl,
     result = SSL_TLSEXT_ERR_NOACK;
 
     if (ctx->alpn != NULL) {
-        result = SSL_select_next_proto(out, 
+        result = SSL_select_next_proto((unsigned char **) out,
                                        outlen,
                                        &ctx->alpn[1], 
                                        (unsigned int) ctx->alpn[0],