Google.protobuf.json_format.MessageToJson changes field names. How to avoid this?

I have a protocol buffer message object. So I want to serialize it this way:

import json
from google.protobuf.json_format import MessageToJson

with open("file.json", 'w') as fjs:
    fjs.write(MessageToJson(message_object))

      

        
        
        
      

    

But it changes the field names of the objects. For example, I had an object like this:

[{
    "id": "333333",
    "creation_timestamp": 2011,
}]

      

        
        
        
      

    

MessageToJson changed its fields to:

[{
  "id": "333333",
  "creationTimestamp": "2011",
}] 

      

        
        
        
      

    

ie creation_timestamp

changes to creationTimestamp

, and 2011

to "2011"

. How to avoid this?