diff --git a/pkgs/development/python-modules/urwidtrees/default.nix b/pkgs/development/python-modules/urwidtrees/default.nix
index b69bb62a875..468420f0e5c 100644
--- a/pkgs/development/python-modules/urwidtrees/default.nix
+++ b/pkgs/development/python-modules/urwidtrees/default.nix
@@ -1,6 +1,7 @@
 { stdenv
 , buildPythonPackage
 , fetchFromGitHub
+, glibcLocales
 , urwid
 }:
 
@@ -17,6 +18,9 @@ buildPythonPackage rec {
 
   propagatedBuildInputs = [ urwid ];
 
+  checkInputs = [ glibcLocales ];
+  LC_ALL="en_US.UTF-8";
+
   meta = with stdenv.lib; {
     description = "Tree widgets for urwid";
     homepage = https://github.com/pazz/urwidtrees;