diff --git a/binaries/data/mods/public/gui/common/network.js b/binaries/data/mods/public/gui/common/network.js
index 0b235af146..1de4c0fa22 100644
--- a/binaries/data/mods/public/gui/common/network.js
+++ b/binaries/data/mods/public/gui/common/network.js
@@ -6,8 +6,9 @@ function getDisconnectReason(id)
 	case 0: return translate("Unknown reason");
 	case 1: return translate("Unexpected shutdown");
 	case 2: return translate("Incorrect network protocol version");
-	case 3: return translate("Game has already started");
-	default: return sprintf(translate("\\[Invalid value %(id)s]"), { id: id });
+	case 3: return translate("Game is loading, please try later");
+	case 4: return translate("Game has already started, no observers allowed");
+	default: return sprintf(translate("\\[Invalid value %(id)s]"), { "id": id });
 	}
 }
 
diff --git a/binaries/data/mods/public/gui/gamesetup/gamesetup.js b/binaries/data/mods/public/gui/gamesetup/gamesetup.js
index 051e728617..d18cf4d0c5 100644
--- a/binaries/data/mods/public/gui/gamesetup/gamesetup.js
+++ b/binaries/data/mods/public/gui/gamesetup/gamesetup.js
@@ -154,6 +154,20 @@ function initMain()
 	mapFilters.list_data = getFilterIds();
 	g_GameAttributes.mapFilter = "default";
 
+	// For singleplayer reduce the size of more options dialog by three options (cheats, rated game, observer late join = 90px)
+	if (!g_IsNetworked)
+	{
+		Engine.GetGUIObjectByName("moreOptions").size = "50%-200 50%-195 50%+200 50%+160";
+		Engine.GetGUIObjectByName("hideMoreOptions").size = "50%-70 310 50%+70 336";
+	}
+	// For non-lobby multiplayergames reduce the size of the dialog by one option (rated game, 30px)
+	else if (g_IsNetworked && !Engine.HasXmppClient())
+	{
+		Engine.GetGUIObjectByName("moreOptions").size = "50%-200 50%-195 50%+200 50%+220";
+		Engine.GetGUIObjectByName("hideMoreOptions").size = "50%-70 370 50%+70 396";
+		Engine.GetGUIObjectByName("optionObserverLateJoin").size = "14 338 94% 366";
+	}
+
 	// Setup controls for host only
 	if (g_IsController)
 	{
@@ -255,6 +269,11 @@ function initMain()
 			updateGameAttributes();
 		};
 
+		Engine.GetGUIObjectByName("observerLateJoin").onPress = function() {
+			g_GameAttributes.settings.ObserverLateJoin = this.checked;
+			updateGameAttributes();
+		};
+
 		Engine.GetGUIObjectByName("disableTreasures").onPress = function() {
 			g_GameAttributes.settings.DisableTreasures = this.checked;
 			updateGameAttributes();
@@ -316,6 +335,7 @@ function initMain()
 	{
 		Engine.GetGUIObjectByName("optionCheats").hidden = false;
 		Engine.GetGUIObjectByName("enableCheats").checked = false;
+		Engine.GetGUIObjectByName("optionObserverLateJoin").hidden = false;
 		g_GameAttributes.settings.CheatsEnabled = false;
 		// Setup ranked option if we are connected to the lobby.
 		if (Engine.HasXmppClient())
@@ -331,6 +351,9 @@ function initMain()
 		{
 			Engine.GetGUIObjectByName("enableCheatsText").hidden = true;
 			Engine.GetGUIObjectByName("enableCheats").hidden = false;
+			Engine.GetGUIObjectByName("observerLateJoinText").hidden = true;
+			Engine.GetGUIObjectByName("observerLateJoin").hidden = false;
+
 			if (Engine.HasXmppClient())
 			{
 				Engine.GetGUIObjectByName("enableRatingText").hidden = true;
@@ -1188,10 +1211,12 @@ function onGameAttributesChange()
 	var populationCap = Engine.GetGUIObjectByName("populationCap");
 	var startingResources = Engine.GetGUIObjectByName("startingResources");
 	var ceasefire = Engine.GetGUIObjectByName("ceasefire");
+	var observerLateJoin = Engine.GetGUIObjectByName("observerLateJoin");
 
 	var numPlayersText= Engine.GetGUIObjectByName("numPlayersText");
 	var mapSizeDesc = Engine.GetGUIObjectByName("mapSizeDesc");
 	var mapSizeText = Engine.GetGUIObjectByName("mapSizeText");
+	var observerLateJoinText = Engine.GetGUIObjectByName("observerLateJoinText");
 	var revealMapText = Engine.GetGUIObjectByName("revealMapText");
 	var exploreMapText = Engine.GetGUIObjectByName("exploreMapText");
 	var disableTreasuresText = Engine.GetGUIObjectByName("disableTreasuresText");
@@ -1222,6 +1247,10 @@ function onGameAttributesChange()
 	}
 	else
 		enableRatingText.caption = "Unknown";
+
+	observerLateJoin.checked = g_GameAttributes.settings.ObserverLateJoin;
+	observerLateJoinText.caption = observerLateJoin.checked ? translate("Yes") : translate("No");
+
 	gameSpeedText.caption = g_GameSpeeds.names[speedIdx];
 	gameSpeedBox.selected = speedIdx;
 	populationCap.selected = (mapSettings.PopulationCap !== undefined && POPULATION_CAP_DATA.indexOf(mapSettings.PopulationCap) != -1 ? POPULATION_CAP_DATA.indexOf(mapSettings.PopulationCap) : POPULATION_CAP_DEFAULTIDX);
diff --git a/binaries/data/mods/public/gui/gamesetup/gamesetup.xml b/binaries/data/mods/public/gui/gamesetup/gamesetup.xml
index 4788977568..dc366903a5 100644
--- a/binaries/data/mods/public/gui/gamesetup/gamesetup.xml
+++ b/binaries/data/mods/public/gui/gamesetup/gamesetup.xml
@@ -270,7 +270,7 @@
 
 			<!-- More Options -->
 			<object hidden="true" name="moreOptionsFade" type="image" z="60" sprite="ModernFade"/>
-			<object name="moreOptions" type="image" sprite="ModernDialog" size="50%-200 50%-195 50%+200 50%+220" z="70" hidden="true">
+			<object name="moreOptions" type="image" sprite="ModernDialog" size="50%-200 50%-195 50%+200 50%+250" z="70" hidden="true">
 				<object style="ModernLabelText" type="text" size="50%-128 -18 50%+128 14">
 					<translatableAttribute id="caption">More Options</translatableAttribute>
 				</object>
@@ -385,12 +385,22 @@
 					</object>
 				</object>
 
+				<object name="optionObserverLateJoin" size="14 368 94% 396" hidden="true">
+					<object size="0 0 40% 28" type="text" hidden="false" style="ModernRightLabelText">
+						<translatableAttribute id="caption">Late Observer Joins:</translatableAttribute>
+					</object>
+					<object name="observerLateJoinText" size="40% 0 100% 28" type="text" style="ModernLeftLabelText"/>
+					<object name="observerLateJoin" size="40%+10 5 40%+30 100%-5" type="checkbox" style="ModernTickBox" hidden="true" tooltip_style="onscreenToolTip">
+						<translatableAttribute id="tooltip">Allow observers to join after the game started.</translatableAttribute>
+					</object>
+				</object>
+
 				<!-- Hide More Options Button -->
 				<object
 					name="hideMoreOptions"
 					type="button"
 					style="StoneButton"
-					size="50%-70 370 50%+70 396"
+					size="50%-70 400 50%+70 426"
 					tooltip_style="onscreenToolTip"
 					hotkey="cancel"
 				>
diff --git a/source/network/NetHost.h b/source/network/NetHost.h
index 402e5bb804..0552617708 100644
--- a/source/network/NetHost.h
+++ b/source/network/NetHost.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2011 Wildfire Games.
+/* Copyright (C) 2015 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -62,6 +62,7 @@ enum NetDisconnectReason
 	NDR_UNKNOWN = 0,
 	NDR_UNEXPECTED_SHUTDOWN,
 	NDR_INCORRECT_PROTOCOL_VERSION,
+	NDR_SERVER_LOADING,
 	NDR_SERVER_ALREADY_IN_GAME
 };
 
diff --git a/source/network/NetMessages.h b/source/network/NetMessages.h
index 83ca5bb351..13a8aaaff0 100644
--- a/source/network/NetMessages.h
+++ b/source/network/NetMessages.h
@@ -28,7 +28,7 @@
 
 #define PS_PROTOCOL_MAGIC				0x5073013f		// 'P', 's', 0x01, '?'
 #define PS_PROTOCOL_MAGIC_RESPONSE		0x50630121		// 'P', 'c', 0x01, '!'
-#define PS_PROTOCOL_VERSION				0x01010006		// Arbitrary protocol
+#define PS_PROTOCOL_VERSION				0x01010007		// Arbitrary protocol
 #define PS_DEFAULT_PORT					0x5073			// 'P', 's'
 
 // Defines the list of message types. The order of the list must not change.
diff --git a/source/network/NetServer.cpp b/source/network/NetServer.cpp
index d5f2204c70..6329c4304e 100644
--- a/source/network/NetServer.cpp
+++ b/source/network/NetServer.cpp
@@ -789,26 +789,40 @@ bool CNetServerWorker::OnAuthenticate(void* context, CFsmEvent* event)
 	CNetServerSession* session = (CNetServerSession*)context;
 	CNetServerWorker& server = session->GetServer();
 
-	CAuthenticateMessage* message = (CAuthenticateMessage*)event->GetParamRef();
+	// Prohibit joins while the game is loading
+	if (server.m_State == SERVER_STATE_LOADING)
+	{
+		LOGMESSAGE("Refused connection while the game is loading");
+		session->Disconnect(NDR_SERVER_LOADING);
+		return true;
+	}
 
+	CAuthenticateMessage* message = (CAuthenticateMessage*)event->GetParamRef();
 	CStrW username = server.DeduplicatePlayerName(SanitisePlayerName(message->m_Name));
 
-	bool isRejoining = false;
+	// Optionally allow observers to join after the game has started
+	bool observerLateJoin = false;
+	ScriptInterface& scriptInterface = server.GetScriptInterface();
+	JSContext* cx = scriptInterface.GetContext();
+	JSAutoRequest rq(cx);
+	JS::RootedValue settings(cx);
+	scriptInterface.GetProperty(server.m_GameAttributes.get(), "settings", &settings);
+	if (scriptInterface.HasProperty(settings, "ObserverLateJoin"))
+		scriptInterface.GetProperty(settings, "ObserverLateJoin", observerLateJoin);
 
+	// If the game has already started, only allow rejoins
+	bool isRejoining = false;
 	if (server.m_State != SERVER_STATE_PREGAME)
 	{
-// 		isRejoining = true; // uncomment this to test rejoining even if the player wasn't connected previously
-
 		// Search for an old disconnected player of the same name
 		// (TODO: if GUIDs were stable, we should use them instead)
-		for (PlayerAssignmentMap::iterator it = server.m_PlayerAssignments.begin(); it != server.m_PlayerAssignments.end(); ++it)
-		{
-			if (!it->second.m_Enabled && it->second.m_Name == username)
-			{
-				isRejoining = true;
-				break;
-			}
-		}
+		isRejoining =
+			observerLateJoin ||
+			std::find_if(
+				server.m_PlayerAssignments.begin(), server.m_PlayerAssignments.end(),
+				[&username] (const std::pair<CStr, PlayerAssignment>& pair)
+				{ return pair.second.m_Enabled && pair.second.m_Name == username; })
+			!= server.m_PlayerAssignments.end();
 
 		// Players who weren't already in the game are not allowed to join now that it's started
 		if (!isRejoining)