diff --git a/hosts/darwin.nix b/hosts/darwin.nix
--- a/hosts/darwin.nix
+++ b/hosts/darwin.nix
@@ -12,6 +12,9 @@ ];
     casks = [
       "hammerspoon"
     ];
-    onActivation.cleanup = "zap";
+    # nix-darwin's cleanup flow is currently emitting a Homebrew flag
+    # combination that your installed brew rejects (`--force-cleanup`).
+    # Leave cleanup disabled during activation until the two agree again.
+    onActivation.cleanup = "none";
   };
 }