diff --git a/openssl/src/rand.rs b/openssl/src/rand.rs
index c1c49e7bda9a585c4631be83807b913cd330a255..9fe222262243a9a9330492f889322ffb7a0e258c 100644
--- a/openssl/src/rand.rs
+++ b/openssl/src/rand.rs
@@ -1,9 +1,27 @@
+//! Cryptographically strong random bytes.
+//!
+//! This module exposes functionality to put cryptographically strong
+//! pseudo-random bytes into a buffer.
+//!
+//! # Examples
+//!
+//! To generate a buffer with cryptographically strong bytes:
+//!
+//! ```
+//! let muf buf = [0; 256]
+//! rand_bytes(&mut buf).unwrap();
+//! ```
+//!
+//! # External OpenSSL Documentation
+//!
+//! [RAND_bytes](https://www.openssl.org/docs/man1.1.0/crypto/RAND_bytes.html)
 use libc::c_int;
 use ffi;
 
 use cvt;
 use error::ErrorStack;
 
+/// Fills buffer with cryptographically strong pseudo-random bytes.
 pub fn rand_bytes(buf: &mut [u8]) -> Result<(), ErrorStack> {
     unsafe {
         ffi::init();