diff --git a/pkgs/development/python-modules/qasm2image/default.nix b/pkgs/development/python-modules/qasm2image/default.nix
index 429159d05d7d..39c7b2055c1b 100644
--- a/pkgs/development/python-modules/qasm2image/default.nix
+++ b/pkgs/development/python-modules/qasm2image/default.nix
@@ -36,6 +36,8 @@ buildPythonPackage rec {
     ${python.interpreter} tests/launch_tests.py
   '';
 
+  LC_ALL="en_US.UTF-8";
+
   meta = {
     description = "A Python module to visualise quantum circuit";
     homepage    = https://github.com/nelimeee/qasm2image;