diff --git a/test/parallel/test-process-env-tz.js b/test/parallel/test-process-env-tz.js
index 25152a9b6c6ce1..da716299c9f622 100644
--- a/test/parallel/test-process-env-tz.js
+++ b/test/parallel/test-process-env-tz.js
@@ -1,5 +1,10 @@
 'use strict';
 
+// Set the locale to a known good value because it affects ICU's date string
+// formatting. Setting LC_ALL needs to happen before the first call to
+// `icu::Locale::getDefault()` because ICU caches the result.
+process.env.LC_ALL = 'C';
+
 const common = require('../common');
 const assert = require('assert');