diff --git a/nixos/tests/discourse.nix b/nixos/tests/discourse.nix
index cfac5f84a62f..35ca083c6c4e 100644
--- a/nixos/tests/discourse.nix
+++ b/nixos/tests/discourse.nix
@@ -30,6 +30,7 @@ import ./make-test-python.nix (
         virtualisation.memorySize = 2048;
         virtualisation.cores = 4;
         virtualisation.useNixStoreImage = true;
+        virtualisation.writableStore = false;
 
         imports = [ common/user-account.nix ];