diff --git a/diffoscope.spec b/diffoscope.spec
index caeca51..4a75023 100644
--- a/diffoscope.spec
+++ b/diffoscope.spec
@@ -120,7 +120,7 @@ sed -i s/test_diff/_disabled_/ tests/comparators/test_berkeley_db.py
 sed -i s/test_compare_non_existing/_disabled_/ tests/comparators/test_berkeley_db.py
 sed -i s/test_diff/_disabled_/ tests/comparators/test_icc.py
 
-export LC_CTYPE=en_US.utf8
+export LC_CTYPE=C.utf8
 export TZ=UTC
 export PYTHONPATH=build/lib/
 py.test-%{python3_version} tests/ -vv || :