diff --git a/nix/modules/nightly-sweep.nix b/nix/modules/nightly-sweep.nix
index 7a91e03..a41f6d7 100644
--- a/nix/modules/nightly-sweep.nix
+++ b/nix/modules/nightly-sweep.nix
@@ -18,7 +18,10 @@ let
   sweep = pkgs.writeShellApplication {
     name = "cc-ci-nightly-sweep";
     # util-linux provides `script` (abra's PTY wrapper for backup/restore TTY ops) — same as cc-ci-run.
-    runtimeInputs = with pkgs; [ abra docker git curl jq gnused gnugrep gnutar coreutils util-linux procps ];
+    # bash: the sweep's mirror_sync shells out to `bash scripts/recipe-mirror-sync.sh`; writeShellApplication
+    # sets a clean PATH limited to runtimeInputs, so bash must be listed (a real timer fire caught its
+    # absence — manual ssh runs had bash on PATH and masked it).
+    runtimeInputs = with pkgs; [ bash abra docker git curl jq gnused gnugrep gnutar coreutils util-linux procps ];
     text = ''
       export HOME=/root
       export PLAYWRIGHT_BROWSERS_PATH=${pkgs.playwright-driver.browsers}