diff --git a/modules/grist.nix b/modules/grist.nix
index abdcd21..db44725 100644
--- a/modules/grist.nix
+++ b/modules/grist.nix
@@ -35,7 +35,7 @@ with lib;
             GRIST_OIDC_IDP_END_SESSION_ENDPOINT = "https://${auth_dn}/logout";
             # Allow self-signed certificates so this example behaves correctly.
             # REMOVE THIS IF HOSTING ON THE INTERNET.
-            NODE_TLS_REJECT_UNAUTHORIZED = 0;
+            NODE_TLS_REJECT_UNAUTHORIZED = "0";
 
             # Forces Grist to only use a single team called 'Example'
             # GRIST_SINGLE_ORG: my-grist-team   # alternatively, GRIST_ORG_IN_PATH: "true" for multi-team operation