diff --git a/nixos/hosts/sunken-ship.nix b/nixos/hosts/sunken-ship.nix
index 768a0df..f7b99b3 100644
--- a/nixos/hosts/sunken-ship.nix
+++ b/nixos/hosts/sunken-ship.nix
@@ -323,6 +323,8 @@
       python-multipart
       mutagen   # tag writeback (enrich.write_tags); needed by the
                 # /enrich/revert endpoint which reuses enrich.py.
+      numpy     # FFT for spectral-rolloff analysis (quality.py); used
+                # by chromaprint-dupe winner picker in --spectral mode.
     ]);
   in {
     description = "Mulbo companion service (uploads, dedup, folders)";