Index: binaries/data/mods/public/simulation/components/ProductionQueue.js
===================================================================
--- binaries/data/mods/public/simulation/components/ProductionQueue.js
+++ binaries/data/mods/public/simulation/components/ProductionQueue.js
@@ -261,6 +261,21 @@
 	// to be possible to add a batch (based on resource costs and length limits).
 	let cmpPlayer = QueryOwnerInterface(this.entity);
 
+	if (!this.queue.length)
+	{
+		let cmpUpgrade = Engine.QueryInterface(this.entity, IID_Upgrade);
+		if (cmpUpgrade && cmpUpgrade.IsUpgrading())
+		{
+			let cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
+			cmpGUIInterface.PushNotification({
+			    "players": [cmpPlayer.GetPlayerID()],
+			    "message": markForTranslation("Entity is being upgraded. Cannot start production."),
+			    "translateMessage": true,
+			});
+			return;
+		}
+	}
+
 	if (this.queue.length < this.MaxQueueSize)
 	{
 
@@ -870,6 +885,11 @@
 		this.CalculateEntitiesList();
 };
 
+ProductionQueue.prototype.HasQueuedProduction = function()
+{
+	return this.queue.length > 0;
+}
+
 ProductionQueue.prototype.OnDisabledTemplatesChanged = function(msg)
 {
 	// If the disabled templates of the player is changed,
Index: binaries/data/mods/public/simulation/components/Upgrade.js
===================================================================
--- binaries/data/mods/public/simulation/components/Upgrade.js
+++ binaries/data/mods/public/simulation/components/Upgrade.js
@@ -228,6 +228,17 @@
 		return false;
 
 	let cmpPlayer = QueryOwnerInterface(this.entity, IID_Player);
+	let cmpProductionQueue = Engine.QueryInterface(this.entity, IID_ProductionQueue);
+	if (cmpProductionQueue && cmpProductionQueue.HasQueuedProduction())
+	{
+		let cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
+		cmpGUIInterface.PushNotification({
+		    "players": [cmpPlayer.GetPlayerID()],
+		    "message": markForTranslation("Entity is producing. Cannot start upgrading."),
+		    "translateMessage": true,
+		});
+		return false;
+	}
 
 	this.expendedResources = this.GetResourceCosts(template);
 	if (!cmpPlayer.TrySubtractResources(this.expendedResources))