diff --git a/src/data_replicator.rs b/src/data_replicator.rs
index 2e1b6ca4d7..18ce3c3dd3 100644
--- a/src/data_replicator.rs
+++ b/src/data_replicator.rs
@@ -1,3 +1,5 @@
+//! The `data_replicator` module implements the replication threads.
+
 use crdt;
 use packet;
 use result::Result;
diff --git a/src/logger.rs b/src/logger.rs
index 88bcc911bf..120e3ff824 100644
--- a/src/logger.rs
+++ b/src/logger.rs
@@ -1,3 +1,6 @@
+//! The `logger` module provides a setup function for `env_logger`. Its only function,
+//! `setup()` may be called multiple times.
+
 use std::sync::{Once, ONCE_INIT};
 extern crate env_logger;
 
diff --git a/src/timing.rs b/src/timing.rs
index 4b0b9ab576..0adcf91cb9 100644
--- a/src/timing.rs
+++ b/src/timing.rs
@@ -1,3 +1,4 @@
+//! The `timing` module provides std::time utility functions.
 use std::time::Duration;
 use std::time::{SystemTime, UNIX_EPOCH};