diff --git a/ChangeLog b/ChangeLog
index 30a84f1..18a47c8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,8 +3,9 @@
 = mbed TLS 2.16.x branch released xxxx-xx-xx
 
 Changes
-   * Clarify how the interface of the CTR_DRBG module relates to
-     NIST SP 800-90A.
+   * Clarify how the interface of the CTR_DRBG and HMAC modules relates to
+     NIST SP 800-90A. In particular CTR_DRBG requires an explicit nonce
+     to achieve a 256-bit strength if MBEDTLS_ENTROPY_FORCE_SHA256 is set.
 
 = mbed TLS 2.16.3 branch released 2019-09-06