This actually needs `wtimeout` handling as well. On MongoDB 2.4, `ensureIndex()` will perform and insert operation on `system.indexes`. In 2.6+, the [createIndexes](http://docs.mongodb.org/manual/reference/command/createIndexes/) command is used. I've updated the driver documentation to clarify this in http://svn.php.net/viewvc?view=revision&revision=333382