diff --git a/flake.nix b/flake.nix
index c846d21..ad432c6 100644
--- a/flake.nix
+++ b/flake.nix
@@ -63,11 +63,10 @@
         version = "0.0.0";
         src = "${self}/pythermostat";
 
-        propagatedBuildInputs =
-          with pkgs.python3Packages; [
-            numpy
-            matplotlib
-          ];
+        propagatedBuildInputs = with pkgs.python3Packages; [
+          numpy
+          matplotlib
+        ];
       };
     in
     {
@@ -95,6 +94,9 @@
             numpy
             matplotlib
           ]);
+        shellHook = ''
+          export PYTHONPATH=`git rev-parse --show-toplevel`/pythermostat:$PYTHONPATH
+        '';
       };
 
       formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt-rfc-style;