diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 47e56e8..23d7b22 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -65,6 +65,13 @@
 /* Faked handshake message identity for HelloRetryRequest. */
 #define MBEDTLS_SSL_TLS1_3_HS_HELLO_RETRY_REQUEST (-MBEDTLS_SSL_HS_SERVER_HELLO)
 
+/* TLS 1.3: Interoperate with peers that support middlebox compatibility
+ * mode, but don't produce the relevant messages ourselves.
+ *
+ * This is always enabled (with effect only when TLS 1.3 is enabled).
+ */
+#define MBEDTLS_SSL_TLS1_3_ACCEPT_COMPATIBILITY_MODE
+
 /*
  * Internal identity of handshake extensions
  */