diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index dc88c4f..7072677 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1518,6 +1518,9 @@
 
     /* Store peer's ECDH/FFDH public key. */
     if (peerkey_len > sizeof(handshake->xxdh_psa_peerkey)) {
+        MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid public key length: %u > %" MBEDTLS_PRINTF_SIZET,
+                                  (unsigned) peerkey_len,
+                                  sizeof(handshake->xxdh_psa_peerkey)));
         return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
     }
     memcpy(handshake->xxdh_psa_peerkey, p, peerkey_len);