Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/MongoDocumentStore.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/MongoDocumentStore.java	(revision 1742265)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/mongo/MongoDocumentStore.java	(working copy)
@@ -1002,7 +1002,7 @@
             T oldDoc = oldDocs.get(id);
             DBObject update;
             if (oldDoc == null) {
-                query.not().exists(Document.MOD_COUNT);
+                query.and(Document.MOD_COUNT).exists(false);
                 update = createUpdate(updateOp, true);
             } else {
                 query.and(Document.MOD_COUNT).is(oldDoc.getModCount());