diff --git a/mongoengine/document.py b/mongoengine/document.py
index 109f8f82..7d03bd60 100644
--- a/mongoengine/document.py
+++ b/mongoengine/document.py
@@ -195,7 +195,9 @@ class Document(BaseDocument):
 
             # Ensure indexes on the collection unless auto_create_index was
             # set to False.
-            if cls._meta.get('auto_create_index', True):
+            # Also there is no need to ensure indexes on slave.
+            if cls._meta.get('auto_create_index', True) and\
+                    db.client.is_primary:
                 cls.ensure_indexes()
 
         return cls._collection