diff --git a/src/java/davmail/exchange/ExchangeSession.java b/src/java/davmail/exchange/ExchangeSession.java
index f9c57330..37bce286 100644
--- a/src/java/davmail/exchange/ExchangeSession.java
+++ b/src/java/davmail/exchange/ExchangeSession.java
@@ -1189,7 +1189,9 @@ public class ExchangeSession {
 
         String searchQuery = "Select \"DAV:getetag\"" +
                 "                FROM Scope('SHALLOW TRAVERSAL OF \"" + calendarUrl + "\"')\n" +
-                "                WHERE (\"urn:schemas:calendar:instancetype\" = 1\n" +
+                "                WHERE (" +
+                "                       \"urn:schemas:calendar:instancetype\" is null OR" +
+                "                       \"urn:schemas:calendar:instancetype\" = 1\n" +
                 "                OR (\"urn:schemas:calendar:instancetype\" = 0\n" +
                 dateCondition +
                 "                )) AND \"DAV:contentclass\" = 'urn:content-classes:appointment'\n" +