diff --git a/lib/mv/vereinfacht/client.ex b/lib/mv/vereinfacht/client.ex
index e7ca04c..3cbba71 100644
--- a/lib/mv/vereinfacht/client.ex
+++ b/lib/mv/vereinfacht/client.ex
@@ -92,10 +92,13 @@ defmodule Mv.Vereinfacht.Client do
 
   @sync_timeout_ms 5_000
 
+  # Resolved at compile time so Mix is never called at runtime (Mix is not available in releases).
+  @env Mix.env()
+
   # In test, skip retries so sync fails fast when no API is running (avoids log spam and long waits).
   defp req_http_options do
     opts = [receive_timeout: @sync_timeout_ms]
-    if Mix.env() == :test, do: [retry: false] ++ opts, else: opts
+    if @env == :test, do: [retry: false] ++ opts, else: opts
   end
 
   defp post_and_parse_contact(url, body, api_key) do