diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index 51867e8..7081070 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -541,6 +541,8 @@
  * They are defined in _Standards for Efficient Cryptography_,
  * _SEC 2: Recommended Elliptic Curve Domain Parameters_.
  * https://www.secg.org/sec2-v2.pdf
+ *
+ * \note For secp224k1, the bit-size is 225 (size of a private value).
  */
 #define PSA_ECC_FAMILY_SECP_K1           ((psa_ecc_family_t) 0x17)