diff --git a/include/mbedtls/ssl_ciphersuites.h b/include/mbedtls/ssl_ciphersuites.h
index 62c138d3a..a707132e8 100644
--- a/include/mbedtls/ssl_ciphersuites.h
+++ b/include/mbedtls/ssl_ciphersuites.h
@@ -304,13 +304,21 @@ typedef enum {
 #define MBEDTLS_SSL_HANDSHAKE_WITH_CERT_ENABLED
 #endif
 
-/* Key exchanges allowing client certificate requests */
+/* Key exchanges allowing client certificate requests.
+ *
+ * Note: that's almost the same as MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED
+ * above, except RSA-PSK uses a server certificate but no client cert.
+ *
+ * Note: this difference is specific to TLS 1.2, as with TLS 1.3, things are
+ * more symmetrical: client certs and server certs are either both allowed
+ * (Ephemeral mode) or both disallowed (PSK and PKS-Ephemeral modes).
+ */
 #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)           ||       \
     defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)       ||       \
-    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)      ||       \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)     ||       \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)   ||       \
     defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)    ||       \
-    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
+    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)
 #define MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED
 #endif