Index: binaries/data/mods/public/simulation/components/UnitAI.js
===================================================================
--- binaries/data/mods/public/simulation/components/UnitAI.js
+++ binaries/data/mods/public/simulation/components/UnitAI.js
@@ -531,6 +531,33 @@
 	},
 
 	"Order.Gather": function(msg) {
+		if (!this.CanGather(this.order.data.target))
+		{
+			this.SetNextState("INDIVIDUAL.GATHER.FINDINGNEWTARGET");
+			return;
+		}
+
+		// If the unit is full go to the nearest dropsite instead of trying to gather.
+		// Unless our target is a treasure which we cannot be full enough with (we can't carry treasures).
+		let cmpResourceGatherer = Engine.QueryInterface(this.entity, IID_ResourceGatherer);
+		if (msg.data.type.generic !== "treasure" && cmpResourceGatherer && !cmpResourceGatherer.CanCarryMore(msg.data.type.generic))
+		{
+			let nearestDropsite = this.FindNearestDropsite(msg.data.type.generic);
+			// Oh no, couldn't find any dropsites. Give up on gathering.
+			if (!nearestDropsite)
+			{
+				this.FinishOrder();
+				return;
+			}
+
+			this.PushOrderFront("ReturnResource", {
+				"target": nearestDropsite,
+				"force": false,
+				"type": msg.data.type
+			});
+			return;
+		}
+
 		// If the target is still alive, we need to kill it first
 		if (this.MustKillGatherTarget(this.order.data.target))
 		{
@@ -2449,6 +2476,13 @@
 					// Collect from the target
 					let status = cmpResourceGatherer.PerformGather(this.gatheringTarget);
 
+					// Find a new target if the current one is exhausted.
+					if (status.exhausted)
+					{
+						this.SetNextState("FINDINGNEWTARGET");
+						return;
+					}
+
 					// If we've collected as many resources as possible,
 					// return to the nearest dropsite
 					if (status.filled)
@@ -2458,10 +2492,6 @@
 						{
 							// (Keep this Gather order on the stack so we'll
 							// continue gathering after returning)
-							// However mark our target as invalid if it's exhausted, so we don't waste time
-							// trying to gather from it.
-							if (status.exhausted)
-								this.order.data.target = INVALID_ENTITY;
 							this.PushOrderFront("ReturnResource", { "target": nearestDropsite, "force": false });
 							return;
 						}
@@ -2470,10 +2500,6 @@
 						this.FinishOrder();
 						return;
 					}
-
-					// Find a new target if the current one is exhausted
-					if (status.exhausted)
-						this.SetNextState("FINDINGNEWTARGET");
 				},
 			},