diff --git a/mod/assign/feedback/editpdf/classes/pdf.php b/mod/assign/feedback/editpdf/classes/pdf.php
index 8578bd6fb07..34db6a14c7a 100644
--- a/mod/assign/feedback/editpdf/classes/pdf.php
+++ b/mod/assign/feedback/editpdf/classes/pdf.php
@@ -445,7 +445,7 @@ class pdf extends \FPDI {
             $filename = \escapeshellarg($this->filename);
             $pagenoinc = \escapeshellarg($pageno + 1);
             $command = "$gsexec -q -sDEVICE=png16m -dSAFER -dBATCH -dNOPAUSE -r$imageres -dFirstPage=$pagenoinc -dLastPage=$pagenoinc ".
-                "-dGraphicsAlphaBits=4 -dTextAlphaBits=4 -sOutputFile=$imagefilearg $filename";
+                "-dDOINTERPOLATE -dGraphicsAlphaBits=4 -dTextAlphaBits=4 -sOutputFile=$imagefilearg $filename";
 
             $output = null;
             $result = exec($command, $output);