diff --git a/static/js/ui/vlm.js b/static/js/ui/vlm.js
index fd819db..1cdad69 100644
--- a/static/js/ui/vlm.js
+++ b/static/js/ui/vlm.js
@@ -162,11 +162,17 @@ const VlmUI = {
             body: formData,
         })
         .then(function(r) {
+            if (r.status === 413) {
+                throw new Error('Bild zu gross fuer Upload. Bitte kleineres Bild verwenden.');
+            }
             if (r.status === 429) {
                 throw new Error('Eine Analyse laeuft bereits. Bitte warten.');
             }
             if (!r.ok) {
-                return r.json().then(function(d) { throw new Error(d.detail || 'Fehler ' + r.status); });
+                return r.text().then(function(txt) {
+                    try { var d = JSON.parse(txt); throw new Error(d.detail || 'Fehler ' + r.status); }
+                    catch(e) { if (e.message && !e.message.startsWith('Unexpected')) throw e; throw new Error('Server-Fehler ' + r.status); }
+                });
             }
             return r.json();
         })