diff --git a/mod/assign/submission/comments/lib.php b/mod/assign/submission/comments/lib.php
index 71caab65319..fe6cb76997b 100644
--- a/mod/assign/submission/comments/lib.php
+++ b/mod/assign/submission/comments/lib.php
@@ -43,7 +43,10 @@ function assignsubmission_comments_comment_validate(stdClass $options) {
     $context = $options->context;
 
     require_once($CFG->dirroot . '/mod/assign/locallib.php');
-    $assignment = new assign($context, null, null);
+    static $assignment = null;
+    if (is_null($assignment) || $assignment->get_context() != $context) {
+        $assignment = new assign($context, null, null);
+    }
 
     if ($assignment->get_instance()->id != $submission->assignment) {
         throw new comment_exception('invalidcontext');
@@ -71,7 +74,10 @@ function assignsubmission_comments_comment_permissions(stdClass $options) {
     $context = $options->context;
 
     require_once($CFG->dirroot . '/mod/assign/locallib.php');
-    $assignment = new assign($context, null, null);
+    static $assignment = null;
+    if (is_null($assignment) || $assignment->get_context() != $context) {
+        $assignment = new assign($context, null, null);
+    }
 
     if ($assignment->get_instance()->id != $submission->assignment) {
         throw new comment_exception('invalidcontext');