diff --git a/lib/formslib.php b/lib/formslib.php
index 700821dc1fb..2bf73b6e384 100644
--- a/lib/formslib.php
+++ b/lib/formslib.php
@@ -82,25 +82,25 @@ function form_init_date_js() {
         $function = 'M.form.dateselector.init_date_selectors';
         $config = array(array(
             'firstdayofweek'    => $calendar->get_starting_weekday(),
-            'mon'               => date_format_string(strtotime("Monday"), '%a', 99),
-            'tue'               => date_format_string(strtotime("Tuesday"), '%a', 99),
-            'wed'               => date_format_string(strtotime("Wednesday"), '%a', 99),
-            'thu'               => date_format_string(strtotime("Thursday"), '%a', 99),
-            'fri'               => date_format_string(strtotime("Friday"), '%a', 99),
-            'sat'               => date_format_string(strtotime("Saturday"), '%a', 99),
-            'sun'               => date_format_string(strtotime("Sunday"), '%a', 99),
-            'january'           => date_format_string(strtotime("January 1"), '%B', 99),
-            'february'          => date_format_string(strtotime("February 1"), '%B', 99),
-            'march'             => date_format_string(strtotime("March 1"), '%B', 99),
-            'april'             => date_format_string(strtotime("April 1"), '%B', 99),
-            'may'               => date_format_string(strtotime("May 1"), '%B', 99),
-            'june'              => date_format_string(strtotime("June 1"), '%B', 99),
-            'july'              => date_format_string(strtotime("July 1"), '%B', 99),
-            'august'            => date_format_string(strtotime("August 1"), '%B', 99),
-            'september'         => date_format_string(strtotime("September 1"), '%B', 99),
-            'october'           => date_format_string(strtotime("October 1"), '%B', 99),
-            'november'          => date_format_string(strtotime("November 1"), '%B', 99),
-            'december'          => date_format_string(strtotime("December 1"), '%B', 99)
+            'mon'               => strftime('%a', strtotime("Monday")),
+            'tue'               => strftime('%a', strtotime("Tuesday")),
+            'wed'               => strftime('%a', strtotime("Wednesday")),
+            'thu'               => strftime('%a', strtotime("Thursday")),
+            'fri'               => strftime('%a', strtotime("Friday")),
+            'sat'               => strftime('%a', strtotime("Saturday")),
+            'sun'               => strftime('%a', strtotime("Sunday")),
+            'january'           => strftime('%B', strtotime("January 1")),
+            'february'          => strftime('%B', strtotime("February 1")),
+            'march'             => strftime('%B', strtotime("March 1")),
+            'april'             => strftime('%B', strtotime("April 1")),
+            'may'               => strftime('%B', strtotime("May 1")),
+            'june'              => strftime('%B', strtotime("June 1")),
+            'july'              => strftime('%B', strtotime("July 1")),
+            'august'            => strftime('%B', strtotime("August 1")),
+            'september'         => strftime('%B', strtotime("September 1")),
+            'october'           => strftime('%B', strtotime("October 1")),
+            'november'          => strftime('%B', strtotime("November 1")),
+            'december'          => strftime('%B', strtotime("December 1"))
         ));
         $PAGE->requires->yui_module($module, $function, $config);
         $done = true;