diff --git a/flake.nix b/flake.nix
index 87bc70d..263c2e7 100644
--- a/flake.nix
+++ b/flake.nix
@@ -95,6 +95,16 @@
               claude-code
               ;
           })
+          # commitizen 4.13.9's regression test for the invalid-command error
+          # message asserts argparse's older, unquoted "invalid choice" wording;
+          # the argparse in Python 3.13 quotes each choice, so the fixture no
+          # longer matches and the checkPhase fails. The package itself is fine
+          # -- deselect just that test. Drop once nixpkgs updates the fixture.
+          (_final: prev: {
+            commitizen = prev.commitizen.overridePythonAttrs (old: {
+              disabledTests = (old.disabledTests or [ ]) ++ [ "test_invalid_command" ];
+            });
+          })
         ];
 
         # Unfree packages permitted to be built (replaces blanket allowUnfree).