diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index 5680a0b..e0126cc 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -66,6 +66,7 @@
 /*
  * Generate/update a key
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_ticket_gen_key( mbedtls_ssl_ticket_context *ctx,
                                unsigned char index )
 {
@@ -96,6 +97,7 @@
 /*
  * Rotate/generate keys if necessary
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_ticket_update_keys( mbedtls_ssl_ticket_context *ctx )
 {
 #if !defined(MBEDTLS_HAVE_TIME)