diff -r bb8a6df5ecba -r 11cd6e034fd3 mod_auth_external/mod_auth_external.lua
--- a/mod_auth_external/mod_auth_external.lua	Thu Aug 29 23:35:42 2019 +0200
+++ b/mod_auth_external/mod_auth_external.lua	Fri Aug 30 13:28:30 2019 +0100
@@ -30,6 +30,7 @@
 
 
 if not blocking then
+	assert(server.event, "External auth non-blocking mode requires libevent installed and enabled");
 	log("debug", "External auth in non-blocking mode, yay!")
 	waiter, guard = async.waiter, async.guarder();
 elseif auth_processes > 1 then