diff --git a/default.nix b/default.nix
index 2011669bf..d20036ae9 100644
--- a/default.nix
+++ b/default.nix
@@ -3,5 +3,8 @@
   pkgs.stdenv.mkDerivation {
     name = "darker-test";
     buildInputs = [ pkgs.python311 pkgs.git ];
+    environment = {
+      PY_IGNORE_IMPORTMISMATCH = "1";
+    };
   }
 )