diff --git a/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java b/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
index 027b7b6..002afb0 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
@@ -50,7 +50,7 @@
         if(bookId == null){
             bookId = 0;
         }
-        else if(!bookManager.getBooks(accountId).containsKey(bookId))return null;
+        else if(!bookManager.getBooks(accountId).containsKey(bookId) || bookId.equals(0))return null;
 
         if(!schedules.containsKey(accountId)){
             schedules.put(accountId, new HashMap<>());
@@ -102,7 +102,7 @@
         if(newBookId == null){
             newBookId = 0;
         }
-        else if(!bookManager.getBooks(accountId).containsKey(newBookId))return -1;
+        else if(!bookManager.getBooks(accountId).containsKey(newBookId) || newBookId.equals(0))return -1;
         schedules.get(accountId).get(year).get(month).get(day).get(scheduleId).setBookId(newBookId);
 
         return 1;