diff --git a/magisch_corvee_script.py b/magisch_corvee_script.py
index 4ee044d..c29a1f5 100755
--- a/magisch_corvee_script.py
+++ b/magisch_corvee_script.py
@@ -1,5 +1,5 @@
 #! /usr/bin/env nix-shell
-#!nix-shell -i python3 -p python python3Packages.pyyaml glpk
+#!nix-shell -i python3 -p python3 python3Packages.pyyaml glpk -I nixpkgs=flake:nixpkgs
 import sys
 import yaml
 import re