--- a/plugins/mod_c2s.lua	Wed May 30 21:33:53 2018 +0100
+++ b/plugins/mod_c2s.lua	Wed May 30 21:55:09 2018 +0100
@@ -49,12 +49,19 @@
 
 function stream_callbacks.streamopened(session, attr)
 	local send = session.send;
-	session.host = nameprep(attr.to);
-	if not session.host then
+	local host = nameprep(attr.to);
+	if not host then
 		session:close{ condition = "improper-addressing",
 			text = "A valid 'to' attribute is required on stream headers" };
 		return;
 	end
+	if not session.host then
+		session.host = host;
+	elseif session.host ~= host then
+		session:close{ condition = "not-authorized",
+			text = "The 'to' attribute must remain the same across stream restarts" };
+		return;
+	end
 	session.version = tonumber(attr.version) or 0;
 	session.streamid = uuid_generate();
 	(session.log or session)("debug", "Client sent opening <stream:stream> to %s", session.host);