diff --git a/src/server.c b/src/server.c
index 376c797..702c307 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1651,7 +1651,7 @@
 	{ "pool-low-conn",       srv_parse_pool_low_conn,       1,  1,  1 }, /* Set the min number of orphan idle connecbefore being allowed to pick from other threads */
 	{ "pool-max-conn",       srv_parse_pool_max_conn,       1,  1,  1 }, /* Set the max number of orphan idle connections, -1 means unlimited */
 	{ "pool-purge-delay",    srv_parse_pool_purge_delay,    1,  1,  1 }, /* Set the time before we destroy orphan idle connections, defaults to 1s */
-	{ "proto",               srv_parse_proto,               1,  1,  0 }, /* Set the proto to use for all outgoing connections */
+	{ "proto",               srv_parse_proto,               1,  1,  1 }, /* Set the proto to use for all outgoing connections */
 	{ "proxy-v2-options",    srv_parse_proxy_v2_options,    1,  1,  1 }, /* options for send-proxy-v2 */
 	{ "redir",               srv_parse_redir,               1,  1,  0 }, /* Enable redirection mode */
 	{ "resolve-net",         srv_parse_resolve_net,         1,  1,  0 }, /* Set the prefered network range for name resolution */
@@ -4377,6 +4377,13 @@
 		goto out;
 	}
 
+	if (srv->mux_proto) {
+		if (!conn_get_best_mux_entry(srv->mux_proto->token, PROTO_SIDE_BE, be->mode)) {
+			cli_err(appctx, "MUX protocol is not usable for server.");
+			goto out;
+		}
+	}
+
 	srv->per_thr = calloc(global.nbthread, sizeof(*srv->per_thr));
 	if (!srv->per_thr) {
 		cli_err(appctx, "failed to allocate per-thread lists for server.");