diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 617bdc7..2c30855 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -379,7 +379,29 @@
                                      const unsigned char *random, size_t rlen,
                                      unsigned char *dstbuf, size_t dlen );
 
+/* cipher.h exports the maximum IV, key and block length from all
+ * all ciphers enabled in the config, regardless of whether those
+ * ciphers are actually usable in SSL/TLS. Notably, XTS is enabled
+ * in the default configuration and uses 64 Byte keys, but it is
+ * not used for record protection in SSL/TLS.
+ *
+ * In order to prevent unnecessary inflation of key structures,
+ * we introduce SSL-specific variants of the max-{key,block,IV}
+ * macros here which are meant to only take those ciphers into
+ * account which can be negotiated in SSL/TLS.
+ *
+ * Since the current definitions of MBEDTLS_MAX_{KEY|BLOCK|IV}_LENGTH
+ * in cipher.h are rough overapproximations of the real maxima, here
+ * we content ourselves with defining replicating those overapproximations
+ * for the maximum block and IV length, and excluding XTS from the
+ * computation of the maximum key length. */
+#define MBEDTLS_SSL_MAX_BLOCK_LENGTH 16
+#define MBEDTLS_SSL_MAX_IV_LENGTH    16
+#define MBEDTLS_SSL_MAX_KEY_LENGTH   32
+
+
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+
 /**
  * \brief   The data structure holding the cryptographic material (key and IV)
  *          used for record protection in TLS 1.3.
@@ -387,13 +409,13 @@
 struct mbedtls_ssl_key_set
 {
     /*! The key for client->server records. */
-    unsigned char client_write_key[ MBEDTLS_MAX_KEY_LENGTH ];
+    unsigned char client_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
     /*! The key for server->client records. */
-    unsigned char server_write_key[ MBEDTLS_MAX_KEY_LENGTH ];
+    unsigned char server_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
     /*! The IV  for client->server records. */
-    unsigned char client_write_iv[ MBEDTLS_MAX_IV_LENGTH ];
+    unsigned char client_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
     /*! The IV  for server->client records. */
-    unsigned char server_write_iv[ MBEDTLS_MAX_IV_LENGTH ];
+    unsigned char server_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
 
     size_t key_len; /*!< The length of client_write_key and
                      *   server_write_key, in Bytes. */