diff --git a/calendar/event.go b/calendar/event.go
index 286d517..227e2c2 100644
--- a/calendar/event.go
+++ b/calendar/event.go
@@ -39,13 +39,16 @@ func (e *Event) BeforeSave(tx *gorm.DB) (err error) {
 	}
 
 	// test for collide
-	cnt := 0
-	db.Raw(`select count(*) from events e where 
+	cnt := ""
+	db.Raw(`select id from events e where 
 		(? >= "start" and ? <= "end" )
 		or
 		(? >= "start" and ? <= "end"  )
-		and calendar_id = ?`,
+		and calendar_id = ? limit 1`,
 		e.End, e.End, e.Start, e.Start, e.CalendarID).Scan(&cnt)
+	if cnt != "" {
+		return errors.New(500, "event collide with existing")
+	}
 
 	return
 }