diff --git a/calendar/lib.php b/calendar/lib.php
index 7fed0c0ee76..ede82803316 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -110,6 +110,16 @@ define('CALENDAR_IMPORT_EVENT_UPDATED',  1);
  */
 define('CALENDAR_IMPORT_EVENT_INSERTED', 2);
 
+/**
+ * CALENDAR_SUBSCRIPTION_UPDATE - Used to represent update action for subscriptions in various forms.
+ */
+define('CALENDAR_SUBSCRIPTION_UPDATE', 1);
+
+/**
+ * CALENDAR_SUBSCRIPTION_REMOVE - Used to represent remove action for subscriptions in various forms.
+ */
+define('CALENDAR_SUBSCRIPTION_REMOVE', 2);
+
 /**
  * Return the days of the week
  *
@@ -2914,17 +2924,13 @@ function calendar_add_icalendar_event($event, $courseid, $subscriptionid) {
  * @return string A log of the import progress, including errors
  */
 function calendar_process_subscription_row($subscriptionid, $pollinterval, $action) {
-    global $DB;
 
     // Fetch the subscription from the database making sure it exists.
     $sub = calendar_get_subscription($subscriptionid);
 
-    $strupdate = get_string('update');
-    $strremove = get_string('remove');
-
     // Update or remove the subscription, based on action.
     switch ($action) {
-        case $strupdate:
+        case CALENDAR_SUBSCRIPTION_UPDATE:
             // Skip updating file subscriptions.
             if (empty($sub->url)) {
                 break;
@@ -2935,7 +2941,7 @@ function calendar_process_subscription_row($subscriptionid, $pollinterval, $acti
             // Update the events.
             return "<p>".get_string('subscriptionupdated', 'calendar', $sub->name)."</p>" . calendar_update_subscription_events($subscriptionid);
 
-        case $strremove:
+        case CALENDAR_SUBSCRIPTION_REMOVE:
             calendar_delete_subscription($subscriptionid);
             return get_string('subscriptionremoved', 'calendar', $sub->name);
             break;
diff --git a/calendar/managesubscriptions.php b/calendar/managesubscriptions.php
index 21782aaa4d6..06d60b49342 100644
--- a/calendar/managesubscriptions.php
+++ b/calendar/managesubscriptions.php
@@ -33,7 +33,7 @@ $courseid = optional_param('course', SITEID, PARAM_INT);
 // Used for processing subscription actions.
 $subscriptionid = optional_param('id', 0, PARAM_INT);
 $pollinterval  = optional_param('pollinterval', 0, PARAM_INT);
-$action = optional_param('action', '', PARAM_ALPHA);
+$action = optional_param('action', '', PARAM_INT);
 
 $url = new moodle_url('/calendar/managesubscriptions.php');
 if ($courseid != SITEID) {
diff --git a/calendar/renderer.php b/calendar/renderer.php
index fbbc848ba97..4fc9a05d76c 100644
--- a/calendar/renderer.php
+++ b/calendar/renderer.php
@@ -836,9 +836,11 @@ class core_calendar_renderer extends plugin_renderer_base {
         $html .= html_writer::empty_tag('input', array('type' => 'hidden', 'name' => 'course', 'value' => $courseid));
         $html .= html_writer::empty_tag('input', array('type' => 'hidden', 'name' => 'id', 'value' => $subscription->id));
         if (!empty($subscription->url)) {
-            $html .= html_writer::empty_tag('input', array('type' => 'submit', 'name' => 'action', 'value' => get_string('update')));
+            $html .= html_writer::tag('button', get_string('update'), array('type'  => 'submit', 'name' => 'action',
+                                                                            'value' => CALENDAR_SUBSCRIPTION_UPDATE));
         }
-        $html .= html_writer::empty_tag('input', array('type' => 'submit', 'name' => 'action', 'value' => get_string('remove')));
+        $html .= html_writer::tag('button', get_string('remove'), array('type'  => 'submit', 'name' => 'action',
+                                                                        'value' => CALENDAR_SUBSCRIPTION_REMOVE));
         $html .= html_writer::end_tag('div');
         $html .= html_writer::end_tag('form');
         return $html;