diff --git a/deploy/nginx-m1.conf b/deploy/nginx-m1.conf
index dae7fe7..d086807 100644
--- a/deploy/nginx-m1.conf
+++ b/deploy/nginx-m1.conf
@@ -6,8 +6,10 @@ server {
 
     # SPA: fall back to index.html for any path
     # Proxy API calls to the FastAPI backend (M3+)
+    # Use variable to defer DNS resolution (docker service name "fastapi")
     location /api/ {
-        proxy_pass http://fastapi:8000;
+        set $fastapi_upstream fastapi;
+        proxy_pass http://$fastapi_upstream:8000;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection 'upgrade';