Index: binaries/data/mods/public/simulation/components/GuiInterface.js
===================================================================
--- binaries/data/mods/public/simulation/components/GuiInterface.js
+++ binaries/data/mods/public/simulation/components/GuiInterface.js
@@ -1894,7 +1894,8 @@
 	if (!data.firstMarket || !data.secondMarket)
 		return null;
 
-	return CalculateTraderGain(data.firstMarket, data.secondMarket, data.template);
+	let cmpMarket = QueryMiragedInterface(data.firstMarket, IID_Market);
+	return cmpMarket && cmpMarket.CalculateTraderGain(data.secondMarket, data.template);
 };
 
 GuiInterface.prototype.GetTradingDetails = function(player, data)
Index: binaries/data/mods/public/simulation/components/Market.js
===================================================================
--- binaries/data/mods/public/simulation/components/Market.js
+++ binaries/data/mods/public/simulation/components/Market.js
@@ -74,6 +74,70 @@
 	}
 };
 
+Market.prototype.CalculateTraderGain = function(secondMarket, traderTemplate, trader)
+{
+	let cmpMarket2 = QueryMiragedInterface(secondMarket, IID_Market);
+	if (!cmpMarket2)
+		return null;
+
+	let cmpMarket1Player = QueryOwnerInterface(this.entity);
+	let cmpMarket2Player = QueryOwnerInterface(secondMarket);
+	if (!cmpMarket1Player || !cmpMarket2Player)
+		return null;
+
+	let cmpFirstMarketPosition = Engine.QueryInterface(this.entity, IID_Position);
+	let cmpSecondMarketPosition = Engine.QueryInterface(secondMarket, IID_Position);
+	if (!cmpFirstMarketPosition || !cmpFirstMarketPosition.IsInWorld() ||
+	   !cmpSecondMarketPosition || !cmpSecondMarketPosition.IsInWorld())
+		return null;
+	let firstMarketPosition = cmpFirstMarketPosition.GetPosition2D();
+	let secondMarketPosition = cmpSecondMarketPosition.GetPosition2D();
+
+	let mapSize = Engine.QueryInterface(SYSTEM_ENTITY, IID_Terrain).GetMapSize();
+	let gainMultiplier = TradeGainNormalization(mapSize);
+	if (trader)
+	{
+		let cmpTrader = Engine.QueryInterface(trader, IID_Trader);
+		if (!cmpTrader)
+			return null;
+		gainMultiplier *= cmpTrader.GetTraderGainMultiplier();
+	}
+	// Called from the gui, modifications already applied.
+	else
+	{
+		if (!traderTemplate || !traderTemplate.GainMultiplier)
+			return null;
+		gainMultiplier *= traderTemplate.GainMultiplier;
+	}
+
+	let gain = {};
+
+	// Calculate ordinary Euclidean distance between markets.
+	// We don't use pathfinder, because ordinary distance looks more fair.
+	let distanceSq = firstMarketPosition.distanceToSquared(secondMarketPosition);
+	// We calculate gain as square of distance to encourage trading between remote markets
+	// and gainMultiplier corresponds to the gain for a 100m distance
+	gain.traderGain = Math.round(gainMultiplier * TradeGain(distanceSq, mapSize));
+
+	gain.market1Owner = cmpMarket1Player.GetPlayerID();
+	gain.market2Owner = cmpMarket2Player.GetPlayerID();
+	// If trader undefined, the trader owner is supposed to be the same as the first market.
+	let cmpPlayer = trader ? QueryOwnerInterface(trader) : cmpMarket1Player;
+	if (!cmpPlayer)
+		return null;
+	gain.traderOwner = cmpPlayer.GetPlayerID();
+
+	if (gain.market1Owner != gain.market2Owner)
+	{
+		let internationalBonus1 = this.GetInternationalBonus();
+		let internationalBonus2 = cmpMarket2.GetInternationalBonus();
+		gain.market1Gain = Math.round(gain.traderGain * internationalBonus1);
+		gain.market2Gain = Math.round(gain.traderGain * internationalBonus2);
+	}
+
+	return gain;
+};
+
 Market.prototype.OnDiplomacyChanged = function(msg)
 {
 	this.UpdateTraders(false);
@@ -142,6 +206,8 @@
 	}
 };
 
+MarketMirage.prototype.CalculateTraderGain = Market.prototype.CalculateTraderGain;
+
 Engine.RegisterGlobal("MarketMirage", MarketMirage);
 
 Market.prototype.Mirage = function(mirageID, miragePlayer)
Index: binaries/data/mods/public/simulation/components/Trader.js
===================================================================
--- binaries/data/mods/public/simulation/components/Trader.js
+++ binaries/data/mods/public/simulation/components/Trader.js
@@ -31,7 +31,8 @@
 
 Trader.prototype.CalculateGain = function(currentMarket, nextMarket)
 {
-	let gain = CalculateTraderGain(currentMarket, nextMarket, this.template, this.entity);
+	let cmpMarket = QueryMiragedInterface(currentMarket, IID_Market);
+	let gain = cmpMarket && cmpMarket.CalculateTraderGain(nextMarket, this.template, this.entity);
 	if (!gain)	// One of our markets must have been destroyed
 		return null;
 
Index: binaries/data/mods/public/simulation/helpers/TraderGain.js
===================================================================
--- binaries/data/mods/public/simulation/helpers/TraderGain.js
+++ /dev/null
@@ -1,66 +0,0 @@
-function CalculateTraderGain(firstMarket, secondMarket, traderTemplate, trader)
-{
-	let cmpMarket1 = QueryMiragedInterface(firstMarket, IID_Market);
-	let cmpMarket2 = QueryMiragedInterface(secondMarket, IID_Market);
-	if (!cmpMarket1 || !cmpMarket2)
-		return null;
-
-	let cmpMarket1Player = QueryOwnerInterface(firstMarket);
-	let cmpMarket2Player = QueryOwnerInterface(secondMarket);
-	if (!cmpMarket1Player || !cmpMarket2Player)
-		return null;
-
-	let cmpFirstMarketPosition = Engine.QueryInterface(firstMarket, IID_Position);
-	let cmpSecondMarketPosition = Engine.QueryInterface(secondMarket, IID_Position);
-	if (!cmpFirstMarketPosition || !cmpFirstMarketPosition.IsInWorld() ||
-	   !cmpSecondMarketPosition || !cmpSecondMarketPosition.IsInWorld())
-		return null;
-	let firstMarketPosition = cmpFirstMarketPosition.GetPosition2D();
-	let secondMarketPosition = cmpSecondMarketPosition.GetPosition2D();
-
-	let mapSize = Engine.QueryInterface(SYSTEM_ENTITY, IID_Terrain).GetMapSize();
-	let gainMultiplier = TradeGainNormalization(mapSize);
-	if (trader)
-	{
-		let cmpTrader = Engine.QueryInterface(trader, IID_Trader);
-		if (!cmpTrader)
-			return null;
-		gainMultiplier *= cmpTrader.GetTraderGainMultiplier();
-	}
-	else	// Called from the gui, modifications already applied.
-	{
-		if (!traderTemplate || !traderTemplate.GainMultiplier)
-			return null;
-		gainMultiplier *= traderTemplate.GainMultiplier;
-	}
-
-	let gain = {};
-
-	// Calculate ordinary Euclidean distance between markets.
-	// We don't use pathfinder, because ordinary distance looks more fair.
-	let distanceSq = firstMarketPosition.distanceToSquared(secondMarketPosition);
-	// We calculate gain as square of distance to encourage trading between remote markets
-	// and gainMultiplier corresponds to the gain for a 100m distance
-	gain.traderGain = Math.round(gainMultiplier * TradeGain(distanceSq, mapSize));
-
-	gain.market1Owner = cmpMarket1Player.GetPlayerID();
-	gain.market2Owner = cmpMarket2Player.GetPlayerID();
-	// If trader undefined, the trader owner is supposed to be the same as the first market
-	let cmpPlayer = trader ? QueryOwnerInterface(trader) : cmpMarket1Player;
-	if (!cmpPlayer)
-		return null;
-	gain.traderOwner = cmpPlayer.GetPlayerID();
-
-	// If markets belong to different players, add gain from international trading
-	if (gain.market1Owner != gain.market2Owner)
-	{
-		let internationalBonus1 = cmpMarket1.GetInternationalBonus();
-		let internationalBonus2 = cmpMarket2.GetInternationalBonus();
-		gain.market1Gain = Math.round(gain.traderGain * internationalBonus1);
-		gain.market2Gain = Math.round(gain.traderGain * internationalBonus2);
-	}
-
-	return gain;
-}
-
-Engine.RegisterGlobal("CalculateTraderGain", CalculateTraderGain);