diff --git a/CCallback.cpp b/CCallback.cpp
index 54ab49a9d..3b3ff165a 100644
--- a/CCallback.cpp
+++ b/CCallback.cpp
@@ -224,7 +224,7 @@ void CCallback::trade(const CGObjectInstance *market, EMarketMode::EMarketMode m
 	sendRequest(&pack);
 }
 
-void CCallback::trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, std::vector<ui32> id1, std::vector<ui32> id2, std::vector<ui32> val1, const CGHeroInstance *hero)
+void CCallback::trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, const std::vector<ui32> &id1, const std::vector<ui32> &id2, const std::vector<ui32> &val1, const CGHeroInstance *hero)
 {
 	TradeOnMarketplace pack;
 	pack.market = market;
diff --git a/CCallback.h b/CCallback.h
index 76169ffc1..625405396 100644
--- a/CCallback.h
+++ b/CCallback.h
@@ -57,7 +57,7 @@ public:
 	virtual void swapGarrisonHero(const CGTownInstance *town)=0;
 
 	virtual void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, ui32 id1, ui32 id2, ui32 val1, const CGHeroInstance *hero = nullptr)=0; //mode==0: sell val1 units of id1 resource for id2 resiurce
-	virtual void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, std::vector<ui32> id1, std::vector<ui32> id2, std::vector<ui32> val1, const CGHeroInstance *hero = nullptr)=0;
+	virtual void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, const std::vector<ui32> &id1, const std::vector<ui32> &id2, const std::vector<ui32> &val1, const CGHeroInstance *hero = nullptr)=0;
 
 	virtual int selectionMade(int selection, QueryID queryID) =0;
 	virtual int sendQueryReply(const JsonNode & reply, QueryID queryID) =0;
@@ -140,7 +140,7 @@ public:
 	void swapGarrisonHero(const CGTownInstance *town) override;
 	void buyArtifact(const CGHeroInstance *hero, ArtifactID aid) override;
 	void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, ui32 id1, ui32 id2, ui32 val1, const CGHeroInstance *hero = nullptr) override;
-	void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, std::vector<ui32> id1, std::vector<ui32> id2, std::vector<ui32> val1, const CGHeroInstance *hero = nullptr) override;
+	void trade(const CGObjectInstance *market, EMarketMode::EMarketMode mode, const std::vector<ui32> &id1, const std::vector<ui32> &id2, const std::vector<ui32> &val1, const CGHeroInstance *hero = nullptr) override;
 	void setFormation(const CGHeroInstance * hero, bool tight) override;
 	void recruitHero(const CGObjectInstance *townOrTavern, const CGHeroInstance *hero) override;
 	void save(const std::string &fname) override;
diff --git a/server/CGameHandler.cpp b/server/CGameHandler.cpp
index 320baa60c..c0adc75dd 100644
--- a/server/CGameHandler.cpp
+++ b/server/CGameHandler.cpp
@@ -5418,7 +5418,7 @@ void CGameHandler::visitObjectOnTile(const TerrainTile &t, const CGHeroInstance
 	}
 }
 
-bool CGameHandler::sacrificeCreatures(const IMarket *market, const CGHeroInstance *hero, std::vector<SlotID> slot, std::vector<ui32> count)
+bool CGameHandler::sacrificeCreatures(const IMarket *market, const CGHeroInstance *hero, const std::vector<SlotID> &slot, const std::vector<ui32> &count)
 {
 	if (!hero)
 		COMPLAIN_RET("You need hero to sacrifice creature!");
@@ -5459,7 +5459,7 @@ bool CGameHandler::sacrificeCreatures(const IMarket *market, const CGHeroInstanc
 	return true;
 }
 
-bool CGameHandler::sacrificeArtifact(const IMarket * m, const CGHeroInstance * hero, std::vector<ArtifactPosition> slot)
+bool CGameHandler::sacrificeArtifact(const IMarket * m, const CGHeroInstance * hero, const std::vector<ArtifactPosition> &slot)
 {
 	if (!hero)
 		COMPLAIN_RET("You need hero to sacrifice artifact!");
diff --git a/server/CGameHandler.h b/server/CGameHandler.h
index c6197673f..cdc882472 100644
--- a/server/CGameHandler.h
+++ b/server/CGameHandler.h
@@ -204,7 +204,7 @@ public:
 	bool buildBoat( ObjectInstanceID objid );
 	bool setFormation( ObjectInstanceID hid, ui8 formation );
 	bool tradeResources(const IMarket *market, ui32 val, PlayerColor player, ui32 id1, ui32 id2);
-	bool sacrificeCreatures(const IMarket *market, const CGHeroInstance *hero, std::vector<SlotID> slot, std::vector<ui32> count);
+	bool sacrificeCreatures(const IMarket *market, const CGHeroInstance *hero, const std::vector<SlotID> &slot, const std::vector<ui32> &count);
 	bool sendResources(ui32 val, PlayerColor player, Res::ERes r1, PlayerColor r2);
 	bool sellCreatures(ui32 count, const IMarket *market, const CGHeroInstance * hero, SlotID slot, Res::ERes resourceID);
 	bool transformInUndead(const IMarket *market, const CGHeroInstance * hero, SlotID slot);
@@ -287,7 +287,7 @@ public:
 	void handleAttackBeforeCasting(BattleAttack *bat);
 	void handleAfterAttackCasting (const BattleAttack & bat);
 	void attackCasting(const BattleAttack & bat, Bonus::BonusType attackMode, const CStack * attacker);
-	bool sacrificeArtifact(const IMarket * m, const CGHeroInstance * hero, std::vector<ArtifactPosition> slot);
+	bool sacrificeArtifact(const IMarket * m, const CGHeroInstance * hero, const std::vector<ArtifactPosition> &slot);
 	void spawnWanderingMonsters(CreatureID creatureID);
 	void handleCheatCode(std::string & cheat, PlayerColor player, const CGHeroInstance * hero, const CGTownInstance * town, bool & cheated);
 	friend class CVCMIServer;