diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c3132a5..fc35427 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2615,6 +2615,11 @@
  * Enable the CMAC (Cipher-based Message Authentication Code) mode for block
  * ciphers.
  *
+ * \note When #MBEDTLS_CMAC_ALT is active, meaning that the underlying
+ *       implementation of the CMAC algorithm is provided by an alternate
+ *       implementation, that alternate implementation may opt to not support
+ *       AES-192 or 3DES as underlying block ciphers for the CMAC operation.
+ *
  * Module:  library/cmac.c
  *
  * Requires: MBEDTLS_AES_C or MBEDTLS_DES_C