Index: ps/trunk/binaries/data/mods/public/gui/gamesetup/gamesetup.js
===================================================================
--- ps/trunk/binaries/data/mods/public/gui/gamesetup/gamesetup.js
+++ ps/trunk/binaries/data/mods/public/gui/gamesetup/gamesetup.js
@@ -2632,6 +2632,7 @@
 		"players": clients.list,
 		"stunIP": g_StunEndpoint ? g_StunEndpoint.ip : "",
 		"stunPort": g_StunEndpoint ? g_StunEndpoint.port : "",
+		"mods": JSON.stringify(Engine.GetEngineInfo().mods),
 	};
 
 	// Only send the stanza if the relevant settings actually changed
Index: ps/trunk/binaries/data/mods/public/gui/lobby/lobby.js
===================================================================
--- ps/trunk/binaries/data/mods/public/gui/lobby/lobby.js
+++ ps/trunk/binaries/data/mods/public/gui/lobby/lobby.js
@@ -34,13 +34,14 @@
 var g_GameColors = {
 	"init": "0 219 0",
 	"waiting": "255 127 0",
-	"running": "219 0 0"
+	"running": "219 0 0",
+	"incompatible": "gray"
 };
 
 /**
  * Initial sorting order of the gamelist.
  */
-var g_GameStatusOrder = ["init", "waiting", "running"];
+var g_GameStatusOrder = ["init", "waiting", "running", "incompatible"];
 
 /**
  * The playerlist will be assembled using these values.
@@ -1016,6 +1017,9 @@
 				Math.round(playerRatings.reduce((sum, current) => sum + current) / playerRatings.length) :
 				g_DefaultLobbyRating;
 
+		if (!hasSameMods(JSON.parse(game.mods), Engine.GetEngineInfo().mods))
+			game.state = "incompatible";
+
 		return game;
 	}).filter(game => !filterGame(game)).sort((a, b) => {
 		let sortA, sortB;
@@ -1170,7 +1174,16 @@
 	let rating = getRejoinRating(game);
 	let username = rating ? g_Username + " (" + rating + ")" : g_Username;
 
-	if (game.state == "init" || stringifiedTeamListToPlayerData(game.players).some(player => player.Name == username))
+	if (game.state == "incompatible")
+		messageBox(
+			400, 200,
+			translate("Your active mods do not match the mods of this game.") + "\n\n" +
+				comparedModsString(JSON.parse(game.mods), Engine.GetEngineInfo().mods),
+			translate("Incompatible mods"),
+			[translate("Ok")],
+			[null]
+		);
+	else if (game.state == "init" || stringifiedTeamListToPlayerData(game.players).some(player => player.Name == username))
 		joinSelectedGame();
 	else
 		messageBox(
Index: ps/trunk/source/lobby/XmppClient.cpp
===================================================================
--- ps/trunk/source/lobby/XmppClient.cpp
+++ ps/trunk/source/lobby/XmppClient.cpp
@@ -493,7 +493,9 @@
 	JSAutoRequest rq(cx);
 
 	scriptInterface.Eval("([])", ret);
-	const char* stats[] = { "name", "ip", "port", "stunIP", "stunPort", "hostUsername", "state", "nbp", "maxnbp", "players", "mapName", "niceMapName", "mapSize", "mapType", "victoryCondition", "startTime" };
+	const char* stats[] = { "name", "ip", "port", "stunIP", "stunPort", "hostUsername", "state",
+		"nbp", "maxnbp", "players", "mapName", "niceMapName", "mapSize", "mapType",
+		"victoryCondition", "startTime", "mods" };
 	for(const glooxwrapper::Tag* const& t : m_GameList)
 	{
 		JS::RootedValue game(cx);