diff --git a/ChangeLog.d/add-tls-exporter.txt b/ChangeLog.d/add-tls-exporter.txt
index 2b06c5f..1aea653 100644
--- a/ChangeLog.d/add-tls-exporter.txt
+++ b/ChangeLog.d/add-tls-exporter.txt
@@ -2,3 +2,5 @@
    * Add the function mbedtls_ssl_export_keying_material() which allows the
      client and server to extract additional shared symmetric keys from an SSL
      session, according to the TLS-Exporter specification in RFC 8446 and 5705.
+     This requires MBEDTLS_SSL_KEYING_MATERIAL_EXPORT to be defined in
+     mbedtls_config.h.