diff --git a/src/platform/web/ui/session/room/timeline/TextMessageView.js b/src/platform/web/ui/session/room/timeline/TextMessageView.js
index 0a0a75cf..ef4d61d5 100644
--- a/src/platform/web/ui/session/room/timeline/TextMessageView.js
+++ b/src/platform/web/ui/session/room/timeline/TextMessageView.js
@@ -105,6 +105,9 @@ const formatFunction = {
 
 function renderPart(part) {
     const f = formatFunction[part.type];
+    if (!f) {
+        return text(`[unknown part type ${part.type}]`);
+    }
     return f(part);
 }