diff --git a/lib/classes/text.php b/lib/classes/text.php
index 587873e31cd..1ae51cebb01 100644
--- a/lib/classes/text.php
+++ b/lib/classes/text.php
@@ -47,6 +47,8 @@ defined('MOODLE_INTERNAL') || die();
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class core_text {
+    /** @var string Byte order mark for UTF-8 */
+    const UTF8_BOM = "\xef\xbb\xbf";
 
     /**
      * @var string[] Array of strings representing Unicode non-characters
@@ -626,7 +628,7 @@ class core_text {
      * @return string
      */
     public static function trim_utf8_bom($str) {
-        $bom = "\xef\xbb\xbf";
+        $bom = self::UTF8_BOM;
         if (strpos($str, $bom) === 0) {
             return substr($str, strlen($bom));
         }
diff --git a/lib/csvlib.class.php b/lib/csvlib.class.php
index daf8da56f5b..00345879892 100644
--- a/lib/csvlib.class.php
+++ b/lib/csvlib.class.php
@@ -390,6 +390,10 @@ class csv_export_writer {
      * @var string $path  The directory path for storing the temporary csv file.
      */
     var $path;
+    /**
+     * @var boolean $bom  If true prefix file with byte order mark (BOM).
+     */
+    private $bom = false;
     /**
      * @var resource $fp  File pointer for the csv file.
      */
@@ -401,8 +405,9 @@ class csv_export_writer {
      * @param string $delimiter      The name of the character used to seperate fields. Supported types(comma, tab, semicolon, colon, cfg)
      * @param string $enclosure      The character used for determining the enclosures.
      * @param string $mimetype       Mime type of the file that we are exporting.
+     * @param boolean $bom           If true, prefix file with byte order mark.
      */
-    public function __construct($delimiter = 'comma', $enclosure = '"', $mimetype = 'application/download') {
+    public function __construct($delimiter = 'comma', $enclosure = '"', $mimetype = 'application/download', $bom = false) {
         $this->delimiter = $delimiter;
         // Check that the enclosure is a single character.
         if (strlen($enclosure) == 1) {
@@ -412,6 +417,7 @@ class csv_export_writer {
         }
         $this->filename = "Moodle-data-export.csv";
         $this->mimetype = $mimetype;
+        $this->bom = $bom;
     }
 
     /**
@@ -437,6 +443,10 @@ class csv_export_writer {
         if(!isset($this->path)) {
             $this->set_temp_file_path();
             $this->fp = fopen($this->path, 'w+');
+
+            if ($this->bom) {
+                fputs($this->fp, core_text::UTF8_BOM);
+            }
         }
         $delimiter = csv_import_reader::get_delimiter($this->delimiter);
         fputcsv($this->fp, $row, $delimiter, $this->csvenclosure);
diff --git a/report/completion/index.php b/report/completion/index.php
index 73380d7e011..7ca465d9b03 100644
--- a/report/completion/index.php
+++ b/report/completion/index.php
@@ -144,7 +144,7 @@ if ($csv) {
     $shortname = format_string($course->shortname, true, array('context' => $context));
     $shortname = preg_replace('/[^a-z0-9-]/', '_',core_text::strtolower(strip_tags($shortname)));
 
-    $export = new csv_export_writer();
+    $export = new csv_export_writer('comma', '"', 'application/download', $excel);
     $export->set_filename('completion-'.$shortname);
 
 } else {