Custom message type errors

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I am trying to create custom message with Power.msg:

# Power
std_msgs/Int64 voltage48
std_msgs/Int64 voltage12

Everything is good until i try to set a value to underlying variables, example:

 custom_msg::Power power_msgs;
 power_msgs.voltage48 = 0;
 power_msgs.voltage12 = 0;
 power_pub.publish(power_msgs);

This doesn't compile due to error: error: no match for ‘operator=’ (operand types are ‘custom_msgs::Power_<std::allocator<void> >::_voltage48_type {aka std_msgs::Int64_<std::allocator<void> >}’ and ‘int’)

What am I doing wrong?