Index: binaries/data/mods/public/simulation/ai/common-api/entity.js
===================================================================
--- binaries/data/mods/public/simulation/ai/common-api/entity.js
+++ binaries/data/mods/public/simulation/ai/common-api/entity.js
@@ -743,6 +743,12 @@
 		return undefined;
 	},
 
+	"garrisonHolder": function() {
+		if (this._entity.garrisonHolder == INVALID_ENTITY)
+			return undefined;
+		return this._entity.garrisonHolder;
+	},
+
 	"garrisoned": function() { return this._entity.garrisoned; },
 
 	"garrisonedSlots": function() {
Index: binaries/data/mods/public/simulation/ai/petra/garrisonManager.js
===================================================================
--- binaries/data/mods/public/simulation/ai/petra/garrisonManager.js
+++ binaries/data/mods/public/simulation/ai/petra/garrisonManager.js
@@ -94,7 +94,7 @@
 			}
 			else
 			{
-				if (ent.unitAIOrderData().some(order => order.target && order.target == id))
+				if (ent.unitAIOrderData().some(order => order.target && order.target == id))//?
 					continue;
 				if (ent.getMetadata(PlayerID, "garrisonHolder") == id)
 				{
Index: binaries/data/mods/public/simulation/ai/petra/headquarters.js
===================================================================
--- binaries/data/mods/public/simulation/ai/petra/headquarters.js
+++ binaries/data/mods/public/simulation/ai/petra/headquarters.js
@@ -398,7 +398,7 @@
 			if (!ent.position())
 			{
 				// we are autogarrisoned, check that the holder is registered in the garrisonManager
-				let holderId = ent.unitAIOrderData()[0].target;
+				let holderId = ent.garrisonHolder();
 				let holder = gameState.getEntityById(holderId);
 				if (holder)
 					this.garrisonManager.registerHolder(gameState, holder);
Index: binaries/data/mods/public/simulation/components/AIProxy.js
===================================================================
--- binaries/data/mods/public/simulation/components/AIProxy.js
+++ binaries/data/mods/public/simulation/components/AIProxy.js
@@ -106,6 +106,13 @@
 	this.changes.hitpoints = msg.to;
 };
 
+AIProxy.prototype.OnGarrisonedStateChanged = function(msg)
+{
+	if (!this.NotifyChange())
+		return;
+	this.changes.garrisonHolder = msg.holder;
+};
+
 AIProxy.prototype.OnCapturePointsChanged = function(msg)
 {
 	if (!this.NotifyChange())
Index: binaries/data/mods/public/simulation/components/Garrisonable.js
===================================================================
--- binaries/data/mods/public/simulation/components/Garrisonable.js
+++ binaries/data/mods/public/simulation/components/Garrisonable.js
@@ -84,6 +84,10 @@
 	if (cmpPosition)
 		cmpPosition.MoveOutOfWorld();
 
+	Engine.PostMessage(this.entity, MT_GarrisonedStateChanged, {
+		"holder": entity
+	});
+
 	if (renamed)
 		return true;
 
@@ -154,6 +158,10 @@
 	if (cmpAura && cmpAura.HasGarrisonAura())
 		cmpAura.RemoveGarrisonAura(this.holder);
 
+	Engine.PostMessage(this.entity, MT_GarrisonedStateChanged, {
+		"holder": INVALID_ENTITY
+	});
+
 	if (renamed)
 		return true;
 
Index: binaries/data/mods/public/simulation/components/interfaces/Garrisonable.js
===================================================================
--- binaries/data/mods/public/simulation/components/interfaces/Garrisonable.js
+++ binaries/data/mods/public/simulation/components/interfaces/Garrisonable.js
@@ -1 +1,7 @@
 Engine.RegisterInterface("Garrisonable");
+
+/**
+ * Message of the form { "holder": number }
+ * sent from the Garrisonable component whenever the garrisoned state changes.
+ */
+Engine.RegisterMessageType("GarrisonedStateChanged");