diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 81fa514..dc88c4f 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1516,7 +1516,10 @@
     /* Check if key size is consistent with given buffer length. */
     MBEDTLS_SSL_CHK_BUF_READ_PTR(p, end, peerkey_len);
 
-    /* Store peer's ECDH public key. */
+    /* Store peer's ECDH/FFDH public key. */
+    if (peerkey_len > sizeof(handshake->xxdh_psa_peerkey)) {
+        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
+    }
     memcpy(handshake->xxdh_psa_peerkey, p, peerkey_len);
     handshake->xxdh_psa_peerkey_len = peerkey_len;