diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 88f4701..a038121 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -631,6 +631,13 @@
 #error "MBEDTLS_SSL_CID_OUT_LEN_MAX too large (max 255)"
 #endif
 
+#if (  defined(MBEDTLS_SSL_CONF_CID_LEN) &&                     \
+      !defined(MBEDTLS_SSL_CONF_IGNORE_UNEXPECTED_CID) ) ||     \
+    ( !defined(MBEDTLS_SSL_CONF_CID_LEN) &&                     \
+       defined(MBEDTLS_SSL_CONF_IGNORE_UNEXPECTED_CID) )
+#error "MBEDTLS_SSL_CONF_CID_LEN and MBEDTLS_SSL_CONF_IGNORE_UNEXPECTED_CID must be defined simultaneously"
+#endif
+
 #if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT) &&                              \
     ( !defined(MBEDTLS_SSL_TLS_C) || !defined(MBEDTLS_SSL_PROTO_DTLS) )
 #error "MBEDTLS_SSL_DTLS_BADMAC_LIMIT  defined, but not all prerequisites"