diff --git a/shell/default.nix b/shell/default.nix
index 7be40ab..0f48fa6 100644
--- a/shell/default.nix
+++ b/shell/default.nix
@@ -19,7 +19,7 @@
         ];
 
         env = [
-          { name = "PYTHONPATH"; value = "${pythonEnv}/${pythonEnv.sitePackages}"; }
+          { name = "PYTHONPATH"; prefix = "${pythonEnv}/${pythonEnv.sitePackages}"; }
         ];
       };
   };