diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index b91cde6..f557d7f 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1333,6 +1333,15 @@
     cipher_suites_len = MBEDTLS_GET_UINT16_BE(p, 0);
     p += 2;
 
+    /*
+     * The length of the ciphersuite list has to be even.
+     */
+    if (cipher_suites_len & 1) {
+        MBEDTLS_SSL_PEND_FATAL_ALERT(MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR,
+                                     MBEDTLS_ERR_SSL_DECODE_ERROR);
+        return MBEDTLS_ERR_SSL_DECODE_ERROR;
+    }
+
     /* Check we have enough data for the ciphersuite list, the legacy
      * compression methods and the length of the extensions.
      *
@@ -1362,8 +1371,6 @@
         uint16_t cipher_suite;
         const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
 
-        MBEDTLS_SSL_CHK_BUF_READ_PTR(p, cipher_suites_end, 2);
-
         cipher_suite = MBEDTLS_GET_UINT16_BE(p, 0);
         ciphersuite_info = ssl_tls13_validate_peer_ciphersuite(
             ssl, cipher_suite);