diff --git a/library/ssl_cache.c b/library/ssl_cache.c
index fe4f30c..0288479 100644
--- a/library/ssl_cache.c
+++ b/library/ssl_cache.c
@@ -50,6 +50,7 @@
 #endif
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cache_find_entry( mbedtls_ssl_cache_context *cache,
                                  unsigned char const *session_id,
                                  size_t session_id_len,
@@ -124,6 +125,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cache_pick_writing_slot( mbedtls_ssl_cache_context *cache,
                                         unsigned char const *session_id,
                                         size_t session_id_len,