diff --git a/direnvrc b/direnvrc
index 5bfeb85..b57953f 100644
--- a/direnvrc
+++ b/direnvrc
@@ -1,3 +1,4 @@
+# -*- mode: sh -*-
 # shellcheck shell=bash
 
 NIX_DIRENV_VERSION=3.0.4
@@ -467,6 +468,11 @@ use_nix() {
         fi
       fi
 
+      # Some builtin nix tooling depends on this variable being set BEFORE their invocation to change their behavior
+      # (notably haskellPackages.developPackage returns an env if this is set)
+      # This allows us to more closely mimic nix-shell.
+      export IN_NIX_SHELL="impure"
+
       if tmp_profile_rc=$(_nix \
         print-dev-env \
         --profile "$tmp_profile" \