diff --git a/tarpc/src/transport/mod.rs b/tarpc/src/transport/mod.rs
index 41119fc..f666d10 100644
--- a/tarpc/src/transport/mod.rs
+++ b/tarpc/src/transport/mod.rs
@@ -2,6 +2,8 @@ use std::io::{self, Read, Write};
 use std::time::Duration;
 
 /// A factory for creating a listener on a given address.
+/// For TCP, an address might be an IPv4 address; for Unix sockets, it
+/// is just a file name.
 pub trait Transport {
     /// The type of listener that binds to the given address.
     type Listener: Listener;