diff --git a/src/crypto/internal/fips140/drbg/rand.go b/src/crypto/internal/fips140/drbg/rand.go
index e7ab19a4cf..c1a3ea0ae6 100644
--- a/src/crypto/internal/fips140/drbg/rand.go
+++ b/src/crypto/internal/fips140/drbg/rand.go
@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Package drbg provides cryptographically secure random bytes
+// usable by FIPS code. In FIPS mode it uses an SP 800-90A Rev. 1
+// Deterministic Random Bit Generator (DRBG). Otherwise,
+// it uses the operating system's random number generator.
 package drbg
 
 import (