diff --git a/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php b/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
index d604b7395e2..26a9850aecd 100644
--- a/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
+++ b/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
@@ -51,6 +51,7 @@ $string['filter'] = 'Filter comments...';
 $string['generatefeedback'] = 'Generate feedback PDF';
 $string['gotopage'] = 'Go to page';
 $string['green'] = 'Green';
+$string['gsimage'] = 'Ghostscript test image';
 $string['pathtogspathdesc'] = 'Please note that annotate PDF requires the path to ghostscript to be set in {$a}.';
 $string['highlight'] = 'Highlight';
 $string['jsrequired'] = 'JavaScript is required to annotate a PDF. Please enable JavaScript in your browser to use this feature.';
diff --git a/mod/assign/feedback/editpdf/testgs.php b/mod/assign/feedback/editpdf/testgs.php
index 49bddd95df9..4ce3d7ad37e 100644
--- a/mod/assign/feedback/editpdf/testgs.php
+++ b/mod/assign/feedback/editpdf/testgs.php
@@ -55,7 +55,7 @@ switch ($result->status) {
         $msg = get_string('test_ok', 'assignfeedback_editpdf');
         $msg .= html_writer::empty_tag('br');
         $imgurl = new moodle_url($PAGE->url, array('sendimage' => 1));
-        $msg .= html_writer::empty_tag('img', array('src' => $imgurl));
+        $msg .= html_writer::empty_tag('img', array('src' => $imgurl, 'alt' => get_string('gsimage', 'assignfeedback_editpdf')));
         break;
 
     case assignfeedback_editpdf\pdf::GSPATH_ERROR: