diff --git a/compose.yml b/compose.yml
index 425efcd..40856ac 100644
--- a/compose.yml
+++ b/compose.yml
@@ -197,7 +197,7 @@ services:
       - GRAMPSWEB_ADMIN_EMAIL=${GRAMPSWEB_ADMIN_EMAIL}
       - GRAMPSWEB_ADMIN_PASSWORD=${GRAMPSWEB_ADMIN_PASSWORD}
       - GRAMPSWEB_TREE=${GRAMPSWEB_TREE:-Stiftung}
-      - GRAMPSWEB_BASE_URL=${GRAMPSWEB_BASE_URL:-/ahnenforschung}
+      - GRAMPSWEB_BASE_URL=${GRAMPSWEB_BASE_URL:-http://localhost:8090}
       - GRAMPSWEB_CELERY_CONFIG__broker_url=redis://redis:6379/0
       - GRAMPSWEB_CELERY_CONFIG__result_backend=redis://redis:6379/0
       - GRAMPSWEB_RATELIMIT_STORAGE_URI=redis://redis:6379/1
diff --git a/deploy-production/nginx.conf b/deploy-production/nginx.conf
index da57054..7ee8f8e 100644
--- a/deploy-production/nginx.conf
+++ b/deploy-production/nginx.conf
@@ -83,6 +83,8 @@ server {
     }
 
     # GrampsWeb Ahnenforschung
+    # GrampsWeb SPA has <base href="/"> hardcoded — sub_filter rewrites it
+    # so asset URLs resolve under /ahnenforschung/ instead of /
     location /ahnenforschung/ {
         proxy_pass http://127.0.0.1:8090/;
         proxy_set_header Host $host;
@@ -91,7 +93,14 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
         proxy_set_header X-Script-Name /ahnenforschung;
 
-        # WebSocket support (GrampsWeb uses SSE/WS for real-time updates)
+        # Rewrite <base href="/"> to <base href="/ahnenforschung/">
+        # so the SPA loads JS/CSS from the correct subpath
+        proxy_set_header Accept-Encoding "";
+        sub_filter '<base href="/">' '<base href="/ahnenforschung/">';
+        sub_filter_once on;
+        sub_filter_types text/html;
+
+        # WebSocket support
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection "upgrade";