diff --git a/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt b/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt
index 392a91b729..1f2c563be3 100644
--- a/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt
+++ b/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt
@@ -1,2 +1,3 @@
 Bugfix
-   * Fixed undefined behavior in mbedtls_ssl_read if len argument is 0
+   * Fix undefined behavior in mbedtls_ssl_read() and mbedtls_ssl_write() if
+     len argument is 0 and buffer is NULL.