diff --git a/pkgs/development/tools/pypi2nix/default.nix b/pkgs/development/tools/pypi2nix/default.nix
index 70c292365abc..e3d458fc6483 100644
--- a/pkgs/development/tools/pypi2nix/default.nix
+++ b/pkgs/development/tools/pypi2nix/default.nix
@@ -43,7 +43,7 @@ in stdenv.mkDerivation rec {
     mv click-*/click                    $out/pkgs/click
     mv requests-*/requests              $out/pkgs/
 
-    if [ "$IN_NIX_SHELL" != "1" ]; then
+    if [ -z "$IN_NIX_SHELL" ]; then
       if [ -e git-export ]; then
         mv git-export/src/pypi2nix      $out/pkgs/pypi2nix
       else