diff --git a/ChangeLog.d/psa_generate_key_custom.txt b/ChangeLog.d/psa_generate_key_custom.txt
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+API changes
+   * The experimental functions psa_generate_key_ext() and
+     psa_key_derivation_output_key_ext() are no longer declared when compiling
+     in C++. This resolves a build failure under C++ compilers that do not
+     support flexible array members (a C99 feature not adopted by C++).
+     Fixes #9020.
+
+New deprecations
+   * The experimental functions psa_generate_key_ext() and
+     psa_key_derivation_output_key_ext() are deprecated in favor of
+     psa_generate_key_custom() and psa_key_derivation_output_key_custom().
+     They have almost exactly the same interface, but the variable-length
+     data is passed in a separate parameter instead of a flexible array
+     member.