diff --git a/ChangeLog.d/sha384-blocksize.txt b/ChangeLog.d/sha384-blocksize.txt
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+++ b/ChangeLog.d/sha384-blocksize.txt
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+Security
+   * Fix definition of MBEDTLS_MD_MAX_BLOCK_SIZE, which was too
+     small when MBEDTLS_SHA384_C was defined and MBEDTLS_SHA512_C was
+     undefined. Mbed TLS itself was unaffected by this, but user code
+     which used MBEDTLS_MD_MAX_BLOCK_SIZE could be affected. The only
+     release containing this bug was Mbed TLS 3.4.0.