diff --git a/calendar/lib.php b/calendar/lib.php
index 3b4b9b12118..185daa00a61 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -116,7 +116,7 @@ function calendar_get_mini($courses, $groups, $users, $cal_month = false, $cal_y
     }
 
     // This is either a genius idea or an idiot idea: in order to not complicate things, we use this rule: if, after
-    // possibly removing courseid 1 from $courses, there is only one course left, then clicking on a day in the month
+    // possibly removing SITEID from $courses, there is only one course left, then clicking on a day in the month
     // will also set the $SESSION->cal_courses_shown variable to that one course. Otherwise, we 'd need to add extra
     // arguments to this function.
 
@@ -190,10 +190,10 @@ function calendar_get_mini($courses, $groups, $users, $cal_month = false, $cal_y
                     $popupicon = $CFG->modpixpath.'/'.$event->modulename.'/icon.gif';
                     $popupalt  = $event->modulename;
 
-                } else if ($event->courseid == 1) {                                // Site event
+                } else if ($event->courseid == SITEID) {                                // Site event
                     $popupicon = $CFG->pixpath.'/c/site.gif';
                     $popupalt  = '';
-                } else if ($event->courseid > 1 and empty($event->groupid)) {      // Course event
+                } else if ($event->courseid != SITEID && empty($event->groupid)) {      // Course event
                     $popupicon = $CFG->pixpath.'/c/course.gif';
                     $popupalt  = '';
                 } else if ($event->groupid) {                                      // Group event
@@ -302,7 +302,7 @@ function calendar_get_upcoming($courses, $groups, $users, $daysinfuture, $maxeve
     }
 
     // This is either a genius idea or an idiot idea: in order to not complicate things, we use this rule: if, after
-    // possibly removing courseid 1 from $courses, there is only one course left, then clicking on a day in the month
+    // possibly removing SITEID from $courses, there is only one course left, then clicking on a day in the month
     // will also set the $SESSION->cal_courses_shown variable to that one course. Otherwise, we 'd need to add extra
     // arguments to this function.
 
@@ -355,14 +355,12 @@ function calendar_get_upcoming($courses, $groups, $users, $daysinfuture, $maxeve
                 $output[$outkey]->cmid = $module->id;
 
 
-
-            } else if($event->courseid == 1) {                              // Site event
+            } else if($event->courseid == SITEID) {                              // Site event
                 $output[$outkey]->icon = '<img height="16" width="16" src="'.$CFG->pixpath.'/c/site.gif" alt="" style="vertical-align: middle;" />';
                 $output[$outkey]->time = $eventtime;
 
 
-
-            } else if($event->courseid > 1 and !$event->groupid) {          // Course event
+            } else if($event->courseid != SITEID && !$event->groupid) {          // Course event
                 calendar_get_course_cached($coursecache, $event->courseid);
 
                 $output[$outkey]->icon = '<img height="16" width="16" src="'.$CFG->pixpath.'/c/course.gif" alt="" style="vertical-align: middle;" />';
@@ -370,13 +368,11 @@ function calendar_get_upcoming($courses, $groups, $users, $daysinfuture, $maxeve
                 $output[$outkey]->courselink = '<a href="'.$CFG->wwwroot.'/course/view.php?id='.$event->courseid.'">'.$coursecache[$event->courseid]->fullname.'</a>';
 
 
-
             } else if ($event->groupid) {                                    // Group event
                 $output[$outkey]->icon = '<img height="16" width="16" src="'.$CFG->pixpath.'/c/group.gif" alt="" style="vertical-align: middle;" />';
                 $output[$outkey]->time = $eventtime;
 
 
-
             } else if($event->userid) {                                      // User event
                 $output[$outkey]->icon = '<img height="16" width="16" src="'.$CFG->pixpath.'/c/user.gif" alt="" style="vertical-align: middle;" />';
                 $output[$outkey]->time = $eventtime;
@@ -802,10 +798,10 @@ function calendar_events_by_day($events, $month, $year, &$eventsbyday, &$duratio
             $eventsbyday[$eventdaystart][] = $event->id;
 
             // Mark the day as having such an event
-            if($event->courseid == 1 && $event->groupid == 0) {
+            if($event->courseid == SITEID && $event->groupid == 0) {
                 $typesbyday[$eventdaystart]['startglobal'] = true;
             }
-            else if($event->courseid > 1 && $event->groupid == 0) {
+            else if($event->courseid != SITEID  && $event->groupid == 0) {
                 $typesbyday[$eventdaystart]['startcourse'] = true;
             }
             else if($event->groupid) {
@@ -830,10 +826,10 @@ function calendar_events_by_day($events, $month, $year, &$eventsbyday, &$duratio
         // Mark all days between $lowerbound and $upperbound (inclusive) as duration
         for($i = $lowerbound + 1; $i <= $upperbound; ++$i) {
             $durationbyday[$i][] = $event->id;
-            if($event->courseid == 1 && $event->groupid == 0) {
+            if($event->courseid == SITEID && $event->groupid == 0) {
                 $typesbyday[$i]['durationglobal'] = true;
             }
-            else if($event->courseid > 1 && $event->groupid == 0) {
+            else if($event->courseid != SITEID && $event->groupid == 0) {
                 $typesbyday[$i]['durationcourse'] = true;
             }
             else if($event->groupid) {
@@ -932,11 +928,11 @@ function calendar_set_filters(&$courses, &$group, &$user, $courseeventsfrom = NU
 
     if(($SESSION->cal_show_course && $SESSION->cal_show_global) || $ignorefilters) {
         if(is_int($courseeventsfrom)) {
-            $courses = array(1, $courseeventsfrom);
+            $courses = array(SITEID, $courseeventsfrom);
         }
         else if(is_array($courseeventsfrom)) {
             $courses = array_keys($courseeventsfrom);
-            $courses[] = 1;
+            $courses[] = SITEID;
         }
     }
     else if($SESSION->cal_show_course) {
@@ -1007,7 +1003,7 @@ function calendar_edit_event_allowed($event) {
 
     if (isadmin($USER->id)) return true; // Admins are allowed anything
 
-    if ($event->courseid > 1) {
+    if ($event->courseid != SITEID) {
         // Course event, only editing teachers may... edit :P
         if(isteacheredit($event->courseid)) {
             return true;
@@ -1033,7 +1029,7 @@ function calendar_get_default_courses($ignoreref = false) {
     global $USER, $CFG, $SESSION;
 
     if(!empty($SESSION->cal_course_referer) && !$ignoreref) {
-        return array($SESSION->cal_course_referer => 1);
+        return array($SESSION->cal_course_referer => SITEID);
     }
 
     if(empty($USER)) {