diff --git a/www/common/common-thumbnail.js b/www/common/common-thumbnail.js
index ce77ce92f..18e5dff52 100644
--- a/www/common/common-thumbnail.js
+++ b/www/common/common-thumbnail.js
@@ -254,6 +254,12 @@ define([
             var cryptKey = secret.keys && secret.keys.fileKeyStr;
             var key = Nacl.util.decodeBase64(cryptKey);
             FileCrypto.fetchDecryptedMetadata(src, key, function (e, metadata) {
+                if (e) {
+                    if (e === 'XHR_ERROR') { return; }
+                    return console.error(e);
+                }
+                if (!metadata) { return console.error("NO_METADATA"); }
+
                 var v = metadata.thumbnail;
                 if (!v) {
                     v = 'EMPTY';
diff --git a/www/common/cryptpad-common.js b/www/common/cryptpad-common.js
index 0a2ead8f0..a06d77077 100644
--- a/www/common/cryptpad-common.js
+++ b/www/common/cryptpad-common.js
@@ -703,6 +703,9 @@ define([
             if (typeof(Worker) === "undefined") {
                 Feedback.send('NO_WEBWORKER');
             }
+            if (typeof(ServiceWorker) === "undefined") {
+                Feedback.send('NO_SERVICEWORKER');
+            }
 
             Feedback.reportScreenDimensions();
             Feedback.reportLanguage();