How to import a message from a proto file in one directory into another directory's file

I have a protobuf message that I want to use in another file. The structure looks like:

main
- A
-- one.proto
- B
-- two.proto

one.proto contains a message called Foo that I want to use in a message within two.proto:

import "A/one.proto"

message Bar {
  google.protobuf.Int64Value id = 1;
  Foo my_foo = 2;
}

However, there's a red squiggly line under Foo that says Cannot resolve symbol Foo.

How do I import Foo from one.proto so that it is recognized in two.proto?