Be clear about HKDF's applicability for password storage
diff --git a/docs/hazmat/primitives/key-derivation-functions.rst b/docs/hazmat/primitives/key-derivation-functions.rst
index 1937c2e..da47ccd 100644
--- a/docs/hazmat/primitives/key-derivation-functions.rst
+++ b/docs/hazmat/primitives/key-derivation-functions.rst
@@ -128,6 +128,7 @@
`HKDF`_ (HMAC-based Extract-and-Expand Key Derivation Function) is suitable
for deriving keys of a fixed size used for other cryptographic operations.
+ **HKDF should not be used for password storage.**
.. doctest::