diff --git a/static/js/devices.js b/static/js/devices.js
index 689e10c..03ad52d 100644
--- a/static/js/devices.js
+++ b/static/js/devices.js
@@ -13,11 +13,11 @@ function urlStatus(url, cb){
 function checkDownload(url){
   urlStatus(url, function(status) {
     if (status === 200){
-	    var working = false;
+	    document.buildingfw = false;
 	    document.getElementById("download").src=url;
     }
     else {
-	    var working = true;
+	    document.buildingfw = true;
             checkDownload(url);
     }
   });
@@ -101,10 +101,13 @@ function askreboot(device_id) {
 };
 
 function downloadnotice(device_id) {
-	if (!working) {
+	if (!document.buildingfw) {
 		alert("Your file is being prepared. This might take a minute or two, the download will start automatically when the file is ready. You may close this page and click the download button again later to pick the file up – we will store it for you.");
 		checkDownload('/devices/' + device_id + '/download/');
 	};
+	else {
+		alert("You are currently building another firmware. Please wait for this to finish and try again.");
+	};
 };
 
 function showdevices() {
@@ -223,3 +226,5 @@ $("div[id$='-indicator']").each(function() {
 $("#orgaselect").on('change', function() {
 	filtertables();
 });
+
+document.buildingfw = false;