diff --git a/mod/forum/post.php b/mod/forum/post.php
index 1162e6aea95..f2422e5c95b 100644
--- a/mod/forum/post.php
+++ b/mod/forum/post.php
@@ -627,6 +627,9 @@ if ($fromform = $mform_post->get_data()) {
 
         // If the user has access to all groups and they are changing the group, then update the post.
         if ($contextcheck) {
+            if (empty($fromform->groupinfo)) {
+                $fromform->groupinfo = -1;
+            }
             $DB->set_field('forum_discussions' ,'groupid' , $fromform->groupinfo, array('firstpost' => $fromform->id));
         }