diff --git a/js/ui/calendar.js b/js/ui/calendar.js
index 8ccc73d70..ae312c6c0 100644
--- a/js/ui/calendar.js
+++ b/js/ui/calendar.js
@@ -297,7 +297,7 @@ class DBusEventSource extends EventSourceBase {
 
         let changed = false;
         for (const id of ids)
-            changed |= this._events.delete(id);
+            changed = changed || this._events.delete(id);
 
         if (changed)
             this.emit('changed');
@@ -310,7 +310,7 @@ class DBusEventSource extends EventSourceBase {
         let changed = false;
         for (const id of this._events.keys()) {
             if (id.startsWith(sourceUid))
-                changed |= this._events.delete(id);
+                changed = changed || this._events.delete(id);
         }
 
         if (changed)