diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index 71adb93..7986eb2 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -231,6 +231,8 @@
     size_t cache_slots;
     /** Number of slots that are not used for anything. */
     size_t empty_slots;
+    /** Number of slots that are not accessed. */
+    size_t unaccessed_slots;
     /** Largest key id value among open keys in internal persistent storage. */
     psa_key_id_t max_open_internal_key_id;
     /** Largest key id value among open keys in secure elements. */