proto3 nested message creation error

Question

message Action {

    int32 protocol_version = 1;
    int64 uid = 2; 
    int64 object_uid = 3; 
    ServiceType service_type = 4; 
    int32 left_messages = 5;
}

message SendTo {
    extend Action {
        SendTo action = 1010;
    }
}

If I tried to create message like above it gives error service_actions.proto:10:25: "com.sys.test.protocol.Action" does not declare 1010 as an extension number.

Any suggestion how to create such type of messages.