diff --git a/mod/assign/overridedelete.php b/mod/assign/overridedelete.php
index 69d280010ed..b96999a9be9 100644
--- a/mod/assign/overridedelete.php
+++ b/mod/assign/overridedelete.php
@@ -44,6 +44,16 @@ require_login($course, false, $cm);
 // Check the user has the required capabilities to modify an override.
 require_capability('mod/assign:manageoverrides', $context);
 
+if ($override->groupid) {
+    if (!groups_group_visible($override->groupid, $course, $cm)) {
+        print_error('invalidoverrideid', 'assign');
+    }
+} else {
+    if (!groups_user_groups_visible($course, $override->userid, $cm)) {
+        print_error('invalidoverrideid', 'assign');
+    }
+}
+
 $url = new moodle_url('/mod/assign/overridedelete.php', array('id' => $override->id));
 $confirmurl = new moodle_url($url, array('id' => $override->id, 'confirm' => 1));
 $cancelurl = new moodle_url('/mod/assign/overrides.php', array('cmid' => $cm->id));
diff --git a/mod/assign/overrideedit.php b/mod/assign/overrideedit.php
index fd5ca49dba0..9928e8baba5 100644
--- a/mod/assign/overrideedit.php
+++ b/mod/assign/overrideedit.php
@@ -76,6 +76,16 @@ require_capability('mod/assign:manageoverrides', $context);
 if ($overrideid) {
     // Editing an override.
     $data = clone $override;
+
+    if ($override->groupid) {
+        if (!groups_group_visible($override->groupid, $course, $cm)) {
+            print_error('invalidoverrideid', 'assign');
+        }
+    } else {
+        if (!groups_user_groups_visible($course, $override->userid, $cm)) {
+            print_error('invalidoverrideid', 'assign');
+        }
+    }
 } else {
     // Creating a new override.
     $data = new stdClass();