diff --git a/django_mongodb_engine/creation.py b/django_mongodb_engine/creation.py
index bd0667f9..fb47f0b3 100644
--- a/django_mongodb_engine/creation.py
+++ b/django_mongodb_engine/creation.py
@@ -70,7 +70,8 @@ def _handle_newstyle_indexes(self, ensure_index, meta, indexes):
                 # field doesn't need an index.
                 continue
             column = '_id' if field.primary_key else field.column
-            ensure_index(column, unique=field.unique)
+            if not column == '_id':
+                ensure_index(column, unique=field.unique)
 
         # Django unique_together indexes.
         indexes = list(indexes)
@@ -122,10 +123,10 @@ def _handle_oldstyle_indexes(self, ensure_index, meta):
                 # field doesn't need an index.
                 continue
             column = '_id' if field.primary_key else field.column
-            if field.name in descending_indexes:
-                column = [(column, DESCENDING)]
-            ensure_index(column, unique=field.unique,
-                         sparse=field.name in sparse_indexes)
+            if not column == '_id':
+                if field.name in descending_indexes:
+                    column = [(column, DESCENDING)]
+                ensure_index(column, unique=field.unique, sparse=field.name in sparse_indexes)
 
         def create_compound_indexes(indexes, **kwargs):
             # indexes: (field1, field2, ...).