diff --git a/bin/tests/system/isctest/vars/basic.py b/bin/tests/system/isctest/vars/basic.py
index 0d4a9cfa51..e76e5f12c3 100644
--- a/bin/tests/system/isctest/vars/basic.py
+++ b/bin/tests/system/isctest/vars/basic.py
@@ -59,6 +59,6 @@ BASIC_VARS = {
         if not os.getenv("TSAN_OPTIONS", "")
         else ":"  # workaround for GL#4119
     ),
-    "LANG": "C",
+    "LC_ALL": "C",
     "ANS_LOG_LEVEL": "debug",
 }