diff --git a/calendar/lib.php b/calendar/lib.php
index ca520150237..886465a7d28 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -2944,7 +2944,7 @@ function calendar_add_icalendar_event($event, $courseid, $subscriptionid, $timez
     $name = $event->properties['SUMMARY'][0]->value;
     $name = str_replace('\n', '<br />', $name);
     $name = str_replace('\\', '', $name);
-    $name = preg_replace('/\s+/', ' ', $name);
+    $name = preg_replace('/\s+/u', ' ', $name);
 
     $eventrecord = new stdClass;
     $eventrecord->name = clean_param($name, PARAM_NOTAGS);
@@ -2956,7 +2956,7 @@ function calendar_add_icalendar_event($event, $courseid, $subscriptionid, $timez
         $description = clean_param($description, PARAM_NOTAGS);
         $description = str_replace('\n', '<br />', $description);
         $description = str_replace('\\', '', $description);
-        $description = preg_replace('/\s+/', ' ', $description);
+        $description = preg_replace('/\s+/u', ' ', $description);
     }
     $eventrecord->description = $description;
 
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 19a85425564..0f9cc5f7cfa 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -1099,7 +1099,7 @@ function clean_param($param, $type) {
             // Remove some nasties.
             $param = preg_replace('~[[:cntrl:]]|[<>`]~u', '', $param);
             // Convert many whitespace chars into one.
-            $param = preg_replace('/\s+/', ' ', $param);
+            $param = preg_replace('/\s+/u', ' ', $param);
             $param = core_text::substr(trim($param), 0, TAG_MAX_LENGTH);
             return $param;
 
diff --git a/lib/tests/regex_test.php b/lib/tests/regex_test.php
new file mode 100644
index 00000000000..c8dd97eb631
--- /dev/null
+++ b/lib/tests/regex_test.php
@@ -0,0 +1,47 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Test PHP regex capability - this may also serve as an example for devs.
+ *
+ * @package   core
+ * @copyright 2015 Totara Learning Solutions Ltd {@link http://www.totaralms.com/}
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @author    Petr Skoda <petr.skoda@totaralms.com>
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * Test PHP regex capability - this may also serve as an example for devs.
+ *
+ * @package   core
+ * @copyright 2015 Totara Learning Solutions Ltd {@link http://www.totaralms.com/}
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @author    Petr Skoda <petr.skoda@totaralms.com>
+ */
+class core_regex_testcase extends advanced_testcase {
+    public function test_whitespace_replacement_with_u() {
+        $unicode = "Теорія і практика використання системи управління навчанням Moo
+dleКиївський національний університет будівництва і архітектури, 21-22 тра
+вня 2015 р.http://2015.moodlemoot.in.ua/";
+
+        $whitespaced = preg_replace('/\s+/u', ' ', $unicode);
+        $this->assertSame(str_replace("\n", ' ', $unicode), $whitespaced);
+    }
+}
+
+