--- mod_h2/h2_h2.c.old	2015-06-03 17:26:53.838388536 +0200
+++ mod_h2/h2_h2.c	2015-06-03 17:29:28.341950459 +0200
@@ -336,7 +336,14 @@ int h2_h2_pre_conn(conn_rec* c, void *ar
         
         ctx = h2_ctx_get(c, 1);
         if (opt_ssl_register_alpn) {
-            opt_ssl_register_alpn(c, h2_h2_alpn_propose, h2_h2_alpn_negotiated);
+            int rc = opt_ssl_register_alpn(c, h2_h2_alpn_propose,
+                                              h2_h2_alpn_negotiated);
+            if (rc != OK) {
+                ap_log_cerror(APLOG_MARK, APLOG_DEBUG, 0, c,
+                              "h2_h2, pre_connection, no ALPN/NPN configured in mod_ssl "
+                              "(hint: is SSLALPNPreference configured?)");
+                return rc;
+            }
         }
         if (opt_ssl_register_npn) {
             opt_ssl_register_npn(c, h2_h2_npn_advertise, h2_h2_npn_negotiated);