diff --git a/src/libstd/base64.rs b/src/libstd/base64.rs
index cdc15ae1d45..d3452712728 100644
--- a/src/libstd/base64.rs
+++ b/src/libstd/base64.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+//! Base64 binary-to-text encoding
+
 use core::iter;
 use core::str;
 use core::vec;