diff --git a/binaries/data/mods/public/simulation/components/UnitAI.js b/binaries/data/mods/public/simulation/components/UnitAI.js
index a8466361d9..a325f6d1b8 100644
--- a/binaries/data/mods/public/simulation/components/UnitAI.js
+++ b/binaries/data/mods/public/simulation/components/UnitAI.js
@@ -140,7 +140,7 @@ var UnitFsmSpec = {
 
 	"Order.LeaveFoundation": function(msg) {
 		// Default behaviour is to ignore the order since we're busy
-		this.DiscardOrder();
+		return { "discardOrder": true };
 	},
 
 	// Individual orders:
@@ -1368,7 +1368,18 @@ UnitAI.prototype.FinishOrder = function()
 
 	if (this.orderQueue.length)
 	{
-		UnitFsm.ProcessMessage(this, {"type": "Order."+this.order.type, "data": this.order.data});
+		var ret = UnitFsm.ProcessMessage(this,
+			{"type": "Order."+this.order.type, "data": this.order.data}
+		);
+
+		// If the order was rejected then immediately take it off
+		// and process the remaining queue
+		if (ret && ret.discardOrder)
+		{
+			return this.FinishOrder();
+		}
+
+		// Otherwise we've successfully processed a new order
 		return true;
 	}
 	else
@@ -1378,23 +1389,6 @@ UnitAI.prototype.FinishOrder = function()
 	}
 };
 
-/**
- * Call when you want to drop an order inside a FSM order handler.
- * Don't change the FSM state.
- */
-UnitAI.prototype.DiscardOrder = function()
-{
-	if (!this.orderQueue.length)
-		error("DiscardOrder called when order queue is empty");
-
-	this.orderQueue.shift();
-	this.order = this.orderQueue[0];
-	if (!this.orderQueue.length)
-	{
-		this.SetNextState("IDLE");
-	}
-};
-
 /**
  * Add an order onto the back of the queue,
  * and execute it if we didn't already have an order.
@@ -1408,7 +1402,16 @@ UnitAI.prototype.PushOrder = function(type, data)
 	if (this.orderQueue.length == 1)
 	{
 		this.order = order;
-		UnitFsm.ProcessMessage(this, {"type": "Order."+this.order.type, "data": this.order.data});
+		var ret = UnitFsm.ProcessMessage(this,
+			{"type": "Order."+this.order.type, "data": this.order.data}
+		);
+
+		// If the order was rejected then immediately take it off
+		// and process the remaining queue
+		if (ret && ret.discardOrder)
+		{
+			this.FinishOrder();
+		}
 	}
 };
 
@@ -1429,7 +1432,19 @@ UnitAI.prototype.PushOrderFront = function(type, data)
 	{
 		this.orderQueue.unshift(order);
 		this.order = order;
-		UnitFsm.ProcessMessage(this, {"type": "Order."+this.order.type, "data": this.order.data});
+		var ret = UnitFsm.ProcessMessage(this,
+			{"type": "Order."+this.order.type, "data": this.order.data}
+		);
+
+		// If the order was rejected then immediately take it off again;
+		// assume the previous active order is still valid (the short-lived
+		// new order hasn't changed state or anything) so we can carry on
+		// as if nothing had happened
+		if (ret && ret.discardOrder)
+		{
+			this.orderQueue.shift();
+			this.order = this.orderQueue[0];
+		}
 	}
 };
 
diff --git a/binaries/data/mods/public/simulation/helpers/FSM.js b/binaries/data/mods/public/simulation/helpers/FSM.js
index 8b0d60cb30..2b1c795dd5 100644
--- a/binaries/data/mods/public/simulation/helpers/FSM.js
+++ b/binaries/data/mods/public/simulation/helpers/FSM.js
@@ -245,10 +245,13 @@ FSM.prototype.ProcessMessage = function(obj, msg)
 	if (!func)
 	{
 		error("Tried to process unhandled event '" + msg.type + "' in state '" + obj.fsmStateName + "'");
-		return;
+		return undefined;
 	}
-	func.apply(obj, [msg]);
 
+	var ret = func.apply(obj, [msg]);
+
+	// If func called SetNextState then switch into the new state,
+	// and continue switching if the new state's 'enter' called SetNextState again
 	while (obj.fsmNextState)
 	{
 		var nextStateName = this.LookupState(obj.fsmStateName, obj.fsmNextState);
@@ -257,6 +260,8 @@ FSM.prototype.ProcessMessage = function(obj, msg)
 		if (nextStateName != obj.fsmStateName)
 			this.SwitchToNextState(obj, nextStateName);
 	}
+
+	return ret;
 };
 
 FSM.prototype.DeferMessage = function(obj, msg)
@@ -339,6 +344,6 @@ FSM.prototype.SwitchToNextState = function(obj, nextStateName)
 	}
 
 	obj.fsmStateName = nextStateName;
-}
+};
 
 Engine.RegisterGlobal("FSM", FSM);