diff --git a/modules/backrest/default.nix b/modules/backrest/default.nix
index de99b04..04d5463 100644
--- a/modules/backrest/default.nix
+++ b/modules/backrest/default.nix
@@ -10,6 +10,7 @@ let
   # BACKREST_VAR_RESTIC_PASSWORD, which backrest expands as ${RESTIC_PASSWORD}
   # inside the repo env block.
   backrestConfig = builtins.toJSON {
+    version = 4;
     modno = 1;
     instance = "dnsc-server";
     repos = [