diff --git a/calendar/templates/calendar_mini.mustache b/calendar/templates/calendar_mini.mustache
index 53b69439bdb..1ddd0546080 100644
--- a/calendar/templates/calendar_mini.mustache
+++ b/calendar/templates/calendar_mini.mustache
@@ -32,7 +32,7 @@
     }
 }}
 <div{{!
-    }} id="calendar-month-{{date.year}}-{{date.month}}-{{uniqid}}" {{!
+    }} id="calendar-month-{{date.year}}-{{date.mon}}-{{uniqid}}" {{!
     }} data-template="core_calendar/month_mini" {{!
     }} data-includenavigation="{{#includenavigation}}true{{/includenavigation}}{{^includenavigation}}false{{/includenavigation}}"{{!
     }} data-mini="true"{{!
@@ -41,6 +41,6 @@
 </div>
 {{#js}}
 require(['jquery', 'core_calendar/calendar_mini'], function($, CalendarMini) {
-    CalendarMini.init($("#calendar-month-{{date.year}}-{{date.month}}-{{uniqid}}"), !{{initialeventsloaded}});
+    CalendarMini.init($("#calendar-month-{{date.year}}-{{date.mon}}-{{uniqid}}"), !{{initialeventsloaded}});
 });
 {{/js}}
diff --git a/calendar/templates/month_mini.mustache b/calendar/templates/month_mini.mustache
index 4ff26560f2b..7918d98416e 100644
--- a/calendar/templates/month_mini.mustache
+++ b/calendar/templates/month_mini.mustache
@@ -32,7 +32,7 @@
     }
 }}
 <div{{!
-    }} id="month-mini-{{date.year}}-{{date.month}}-{{uniqid}}"{{!
+    }} id="month-mini-{{date.year}}-{{date.mon}}-{{uniqid}}"{{!
     }} class="calendarwrapper"{{!
     }} data-courseid="{{courseid}}"{{!
     }} data-categoryid="{{categoryid}}"{{!
@@ -174,7 +174,7 @@ require([
         M.util.js_pending("month-mini-{{uniqid}}-filterChanged");
         // A filter value has been changed.
         // Find all matching cells in the popover data, and hide them.
-        $("#month-mini-{{date.year}}-{{date.month}}-{{uniqid}}")
+        $("#month-mini-{{date.year}}-{{date.mon}}-{{uniqid}}")
             .find(CalendarSelectors.popoverType[data.type])
             .toggleClass('hidden', !!data.hidden);
         M.util.js_complete("month-mini-{{uniqid}}-filterChanged");