diff --git a/ext/date/tests/bug36599.phpt b/ext/date/tests/bug36599.phpt
new file mode 100644
index 00000000000..b34a7c288fb
--- /dev/null
+++ b/ext/date/tests/bug36599.phpt
@@ -0,0 +1,12 @@
+--TEST--
+Bug #36599 (DATE_W3C format constant incorrect).
+--FILE--
+<?php
+date_default_timezone_set("UTC");
+
+echo date( DATE_ATOM, strtotime( "2006-03-03 08:47:55" ) ), "\n";
+echo date( DATE_W3C,  strtotime( "2006-03-03 08:47:55" ) ), "\n";
+?>
+--EXPECT--
+2006-03-03T08:47:55+00:00
+2006-03-03T08:47:55+00:00