diff --git a/containers/teslamate/default.nix b/containers/teslamate/default.nix
index 024aa6f..e126561 100644
--- a/containers/teslamate/default.nix
+++ b/containers/teslamate/default.nix
@@ -46,6 +46,12 @@ let
     pname = "teslamate";
     inherit version src elixir;
 
+    # Keep the build-generated Erlang cookie in the release. mixRelease
+    # strips it by default (expecting RELEASE_COOKIE at runtime), but the
+    # start script reads releases/COOKIE. teslamate is single-node (no
+    # distributed Erlang exposed), so a baked-in cookie is fine.
+    removeCookie = false;
+
     mixFodDeps = beamPackages.fetchMixDeps {
       pname = "mix-deps-teslamate";
       inherit src version elixir;