diff --git a/inbox.py b/inbox.py
index 82481e356..662127c50 100644
--- a/inbox.py
+++ b/inbox.py
@@ -1387,11 +1387,15 @@ def inboxUpdateCalendar(baseDir: str,handle: str,postJsonObject: {}) -> None:
         if not os.path.isdir(calendarPath+'/'+str(eventYear)):
             os.mkdir(calendarPath+'/'+str(eventYear))
         calendarFilename=calendarPath+'/'+str(eventYear)+'/'+str(eventMonthNumber)+'.txt'
+        postId=postJsonObject['id'].replace('/','#')
+        if os.path.isfile(calendarFilename):
+            if postId in open(calendarFilename).read():
+                return
         calendarFile=open(calendarFilename,'a+')
         if calendarFile:
-            calendarFile.write(postJsonObject['id'].replace('/','#')+'\n')
+            calendarFile.write(postId+'\n')
             calendarFile.close()
-                 
+
 def inboxAfterCapabilities(session,keyId: str,handle: str,messageJson: {}, \
                            baseDir: str,httpPrefix: str,sendThreads: [], \
                            postLog: [],cachedWebfingers: {},personCache: {}, \