diff --git a/include/mbedtls/config_psa.h b/include/mbedtls/config_psa.h
index b469d3c..2a6672e 100644
--- a/include/mbedtls/config_psa.h
+++ b/include/mbedtls/config_psa.h
@@ -606,6 +606,10 @@
 #define PSA_WANT_ALG_GCM 1
 #endif /* MBEDTLS_GCM_C */
 
+/* Enable PSA HKDF algorithm if mbedtls HKDF is supported.
+ * PSA HKDF EXTRACT and PSA HKDF EXPAND have minimal cost when
+ * PSA HKDF is enabled, so enable both algorithms together
+ * with PSA HKDF. */
 #if defined(MBEDTLS_HKDF_C)
 #define MBEDTLS_PSA_BUILTIN_ALG_HMAC 1
 #define PSA_WANT_ALG_HMAC 1