diff --git a/pkgs/development/python-modules/hpack/default.nix b/pkgs/development/python-modules/hpack/default.nix
index a10882417fc0..7e7db13aaec1 100644
--- a/pkgs/development/python-modules/hpack/default.nix
+++ b/pkgs/development/python-modules/hpack/default.nix
@@ -1,6 +1,7 @@
 { stdenv
 , buildPythonPackage
 , fetchPypi
+, glibcLocales
 }:
 
 buildPythonPackage rec {
@@ -12,6 +13,10 @@ buildPythonPackage rec {
     sha256 = "8eec9c1f4bfae3408a3f30500261f7e6a65912dc138526ea054f9ad98892e9d2";
   };
 
+  buildInputs = [ glibcLocales ];
+
+  LANG = "en_US.UTF-8";
+
   meta = with stdenv.lib; {
     description = "Pure-Python HPACK header compression";
     homepage = "http://hyper.rtfd.org";