diff --git a/static/c3lingo.css b/static/c3lingo.css
index 8b5fd5a4b1af0f3f7ca3803b51f2d00016de9fe0..afc83cc80b40b990c2e625c6083a822eca0485f7 100644
--- a/static/c3lingo.css
+++ b/static/c3lingo.css
@@ -186,3 +186,17 @@ body[lang="en"] [data-lang="de"] {
 body[lang="de"] [data-lang="en"] {
   display: none;
 }
+
+.callout {
+  padding: .5em;
+  box-shadow: inset 0 0 0 1px rgba(0, 0, 0, 0.1);
+  border-radius: 3px;
+}
+.callout--error {
+  background-color: rgb(148, 0, 0);
+  color: #fff;
+}
+.callout--success {
+  background-color: rgb(0, 148, 12);
+  color: #fff;
+}
diff --git a/static/index.html b/static/index.html
index 1d02cd110a966b9891017d3269fd45026aca877b..f83289d72c305969db39aeb7d3404d89aa136b9d 100644
--- a/static/index.html
+++ b/static/index.html
@@ -28,6 +28,8 @@
               <p>For listeners sitting in the audience of conference talks as they happen, we provide low-latency translation streams
                 via <a href="https://wiki.mumble.info/">Mumble</a>.</p>
 
+              <p class="callout callout--error">Mumble is currently unavailable. We’re sorry about this and are working hard on a fix.</p>
+
               <p>For this, you'll need a Mumble client. We recommend the following clients:</p>
 
               <ul>
@@ -77,6 +79,8 @@
               <p>Für Menschen, die die Vorträge direkt im Saal verfolgen, bieten wir <a href="https://wiki.mumble.info/">Mumble</a>-Streams
                 mit niedriger Latenz an.</p>
 
+              <p class="callout callout--error">Mumble ist momentan nicht verfügbar. Das tut uns leid; wir arbeiten an der Lösung.</p>
+
               <p>Du benötigst einen Mumble-Client. Wir empfehlen die folgenden Clients:</p>
 
               <ul>