diff --git a/ext/calendar/tests/unixtojd.phpt b/ext/calendar/tests/unixtojd.phpt
index 567a8c25b6b..11edde5f22c 100644
--- a/ext/calendar/tests/unixtojd.phpt
+++ b/ext/calendar/tests/unixtojd.phpt
@@ -4,6 +4,7 @@ unixtojd()
 <?php include 'skipif.inc'; ?>
 --FILE--
 <?php
+putenv('TZ=UTC');
 echo unixtojd(40000). "\n";
 echo unixtojd(1000000000). "\n";
 echo unixtojd(1152459009). "\n";