diff --git a/pkgs/development/python-modules/arelle/default.nix b/pkgs/development/python-modules/arelle/default.nix
index 32c020961f21..2cf14192d09d 100644
--- a/pkgs/development/python-modules/arelle/default.nix
+++ b/pkgs/development/python-modules/arelle/default.nix
@@ -1,7 +1,7 @@
 { gui ? true,
   buildPythonPackage, fetchFromGitHub, lib,
   sphinx_1_2, lxml, isodate, numpy, pytest,
-  tkinter ? null,
+  tkinter ? null, py3to2,
   ... }:
 
 let
@@ -26,6 +26,7 @@ buildPythonPackage {
   buildInputs = [
     sphinx_1_2
     pytest
+    py3to2
   ];
   propagatedBuildInputs = [
     lxml
diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index e1685dc8339a..ec4a6cbbb7ee 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -101,7 +101,7 @@ in {
 
   py3to2 = callPackage ../development/python-modules/3to2 { };
   # Left for backwards compatibility
-  "3to2" = callPackage ../development/python-modules/3to2 { };
+  "3to2" = self.py3to2;
 
   aenum = callPackage ../development/python-modules/aenum { };