diff --git a/frontend/nginx.conf b/frontend/nginx.conf
index 467f2ef..065cca8 100644
--- a/frontend/nginx.conf
+++ b/frontend/nginx.conf
@@ -17,7 +17,9 @@ server {
         proxy_set_header   X-Real-IP         $remote_addr;
         proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
         proxy_set_header   X-Forwarded-Proto $scheme;
-        proxy_read_timeout 60s;
+        # Long enough for the slowest request: a slow local AI model may take up to the 300s
+        # timeout its settings allow.
+        proxy_read_timeout 300s;
         client_max_body_size 512m;
     }
 
diff --git a/frontend/src/api/client.ts b/frontend/src/api/client.ts
index 407e0b1..e7883cd 100644
--- a/frontend/src/api/client.ts
+++ b/frontend/src/api/client.ts
@@ -48,5 +48,11 @@ export async function readErrorMessage(res: Response, fallback: string) {
       return data.detail.trim();
     }
   } catch {}
+  // An HTML page comes from a proxy in front of the backend, not from Thingport.
+  if (/^<(!doctype|html)/i.test(trimmed)) {
+    if (res.status === 504)
+      return "The server took too long to answer, and a proxy in front of Thingport gave up (HTTP 504).";
+    return `${fallback} (HTTP ${res.status})`;
+  }
   return trimmed;
 }