diff --git a/ChangeLog.d/mbedtls_psa_register_se_key.txt b/ChangeLog.d/mbedtls_psa_register_se_key.txt
new file mode 100644
index 0000000..2fc2751
--- /dev/null
+++ b/ChangeLog.d/mbedtls_psa_register_se_key.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Document and enforce the limitation of mbedtls_psa_register_se_key()
+     to persistent keys. Resolves #9253.
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 4842fd4..5b10078 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -4029,13 +4029,18 @@
 //#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256
 
 /** \def MBEDTLS_PSA_KEY_SLOT_COUNT
- * Restrict the PSA library to supporting a maximum amount of simultaneously
- * loaded keys. A loaded key is a key stored by the PSA Crypto core as a
- * volatile key, or a persistent key which is loaded temporarily by the
- * library as part of a crypto operation in flight.
  *
- * If this option is unset, the library will fall back to a default value of
- * 32 keys.
+ * The maximum amount of PSA keys simultaneously in memory. This counts all
+ * volatile keys, plus loaded persistent keys.
+ *
+ * Currently, persistent keys do not need to be loaded all the time while
+ * a multipart operation is in progress, only while the operation is being
+ * set up. This may change in future versions of the library.
+ *
+ * Currently, the library traverses of the whole table on each access to a
+ * persistent key. Therefore large values may cause poor performance.
+ *
+ * This option has no effect when #MBEDTLS_PSA_CRYPTO_C is disabled.
  */
 //#define MBEDTLS_PSA_KEY_SLOT_COUNT 32
 
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index a2d547f..5096748 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -130,6 +130,9 @@
  *
  * \param[out] attributes  The attribute structure to write to.
  * \param key              The persistent identifier for the key.
+ *                         This can be any value in the range from
+ *                         #PSA_KEY_ID_USER_MIN to #PSA_KEY_ID_USER_MAX
+ *                         inclusive.
  */
 static void psa_set_key_id(psa_key_attributes_t *attributes,
                            mbedtls_svc_key_id_t key);
diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index a1b2af7..ea58e87 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -155,6 +155,14 @@
  * specified in \p attributes.
  *
  * \param[in] attributes        The attributes of the existing key.
+ *                              - The lifetime must be a persistent lifetime
+ *                                in a secure element. Volatile lifetimes are
+ *                                not currently supported.
+ *                              - The key identifier must be in the valid
+ *                                range for persistent keys.
+ *                              - The key type and size must be specified and
+ *                                must be consistent with the key material
+ *                                in the secure element.
  *
  * \retval #PSA_SUCCESS
  *         The key was successfully registered.
@@ -709,7 +717,7 @@
  * #PSA_KEY_ID_VENDOR_MIN and #PSA_KEY_ID_VENDOR_MAX and must not intersect
  * with any other set of implementation-chosen key identifiers.
  *
- * This value is part of the library's ABI since changing it would invalidate
+ * This value is part of the library's API since changing it would invalidate
  * the values of built-in key identifiers in applications.
  */
 #define MBEDTLS_PSA_KEY_ID_BUILTIN_MIN          ((psa_key_id_t) 0x7fff0000)
diff --git a/library/common.h b/library/common.h
index 49e2c97..5565b30 100644
--- a/library/common.h
+++ b/library/common.h
@@ -337,17 +337,18 @@
 #endif
 
 /* Always provide a static assert macro, so it can be used unconditionally.
- * It will expand to nothing on some systems.
- * Can be used outside functions (but don't add a trailing ';' in that case:
- * the semicolon is included here to avoid triggering -Wextra-semi when
- * MBEDTLS_STATIC_ASSERT() expands to nothing).
- * Can't use the C11-style `defined(static_assert)` on FreeBSD, since it
+ * It will expand to nothing on some systems. */
+/* Can't use the C11-style `defined(static_assert)` on FreeBSD, since it
  * defines static_assert even with -std=c99, but then complains about it.
  */
 #if defined(static_assert) && !defined(__FreeBSD__)
-#define MBEDTLS_STATIC_ASSERT(expr, msg)    static_assert(expr, msg);
+#define MBEDTLS_STATIC_ASSERT(expr, msg)    static_assert(expr, msg)
 #else
-#define MBEDTLS_STATIC_ASSERT(expr, msg)
+/* Make sure `MBEDTLS_STATIC_ASSERT(expr, msg);` is valid both inside and
+ * outside a function. We choose a struct declaration, which can be repeated
+ * any number of times and does not need a matching definition. */
+#define MBEDTLS_STATIC_ASSERT(expr, msg)                                \
+    struct ISO_C_does_not_allow_extra_semicolon_outside_of_a_function
 #endif
 
 /* Suppress compiler warnings for unused functions and variables. */
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index a580333..21d8420 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1622,11 +1622,11 @@
 }
 
 MBEDTLS_STATIC_ASSERT((MBEDTLS_PSA_KA_MASK_EXTERNAL_ONLY & MBEDTLS_PSA_KA_MASK_DUAL_USE) == 0,
-                      "One or more key attribute flag is listed as both external-only and dual-use")
+                      "One or more key attribute flag is listed as both external-only and dual-use");
 MBEDTLS_STATIC_ASSERT((PSA_KA_MASK_INTERNAL_ONLY & MBEDTLS_PSA_KA_MASK_DUAL_USE) == 0,
-                      "One or more key attribute flag is listed as both internal-only and dual-use")
+                      "One or more key attribute flag is listed as both internal-only and dual-use");
 MBEDTLS_STATIC_ASSERT((PSA_KA_MASK_INTERNAL_ONLY & MBEDTLS_PSA_KA_MASK_EXTERNAL_ONLY) == 0,
-                      "One or more key attribute flag is listed as both internal-only and external-only")
+                      "One or more key attribute flag is listed as both internal-only and external-only");
 
 /** Validate that a key policy is internally well-formed.
  *
@@ -2149,6 +2149,14 @@
         return PSA_ERROR_NOT_SUPPORTED;
     }
 
+    /* Not usable with volatile keys, even with an appropriate location,
+     * due to the API design.
+     * https://github.com/Mbed-TLS/mbedtls/issues/9253
+     */
+    if (PSA_KEY_LIFETIME_IS_VOLATILE(psa_get_key_lifetime(attributes))) {
+        return PSA_ERROR_INVALID_ARGUMENT;
+    }
+
     status = psa_start_key_creation(PSA_KEY_CREATION_REGISTER, attributes,
                                     &slot, &driver);
     if (status != PSA_SUCCESS) {
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index b79c713..1a54420 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -26,6 +26,37 @@
 
 #define ARRAY_LENGTH(array) (sizeof(array) / sizeof(*(array)))
 
+
+
+/* Make sure we have distinct ranges of key identifiers for distinct
+ * purposes. */
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_USER_MIN < PSA_KEY_ID_USER_MAX,
+                      "Empty user key ID range");
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VENDOR_MIN < PSA_KEY_ID_VENDOR_MAX,
+                      "Empty vendor key ID range");
+MBEDTLS_STATIC_ASSERT(MBEDTLS_PSA_KEY_ID_BUILTIN_MIN < MBEDTLS_PSA_KEY_ID_BUILTIN_MAX,
+                      "Empty builtin key ID range");
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MIN < PSA_KEY_ID_VOLATILE_MAX,
+                      "Empty volatile key ID range");
+
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_USER_MAX < PSA_KEY_ID_VENDOR_MIN ||
+                      PSA_KEY_ID_VENDOR_MAX < PSA_KEY_ID_USER_MIN,
+                      "Overlap between user key IDs and vendor key IDs");
+
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VENDOR_MIN <= MBEDTLS_PSA_KEY_ID_BUILTIN_MIN &&
+                      MBEDTLS_PSA_KEY_ID_BUILTIN_MAX <= PSA_KEY_ID_VENDOR_MAX,
+                      "Builtin key identifiers are not in the vendor range");
+
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VENDOR_MIN <= PSA_KEY_ID_VOLATILE_MIN &&
+                      PSA_KEY_ID_VOLATILE_MAX <= PSA_KEY_ID_VENDOR_MAX,
+                      "Volatile key identifiers are not in the vendor range");
+
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MAX < MBEDTLS_PSA_KEY_ID_BUILTIN_MIN ||
+                      MBEDTLS_PSA_KEY_ID_BUILTIN_MAX < PSA_KEY_ID_VOLATILE_MIN,
+                      "Overlap between builtin key IDs and volatile key IDs");
+
+
+
 typedef struct {
     psa_key_slot_t key_slots[MBEDTLS_PSA_KEY_SLOT_COUNT];
     unsigned key_slots_initialized : 1;
@@ -33,6 +64,10 @@
 
 static psa_global_data_t global_data;
 
+MBEDTLS_STATIC_ASSERT(ARRAY_LENGTH(global_data.key_slots) <=
+                      PSA_KEY_ID_VOLATILE_MAX - PSA_KEY_ID_VOLATILE_MIN + 1,
+                      "The key slot array is larger than the volatile key ID range");
+
 int psa_is_valid_key_id(mbedtls_svc_key_id_t key, int vendor_ok)
 {
     psa_key_id_t key_id = MBEDTLS_SVC_KEY_ID_GET_KEY_ID(key);
diff --git a/tests/suites/test_suite_psa_crypto_driver_wrappers.data b/tests/suites/test_suite_psa_crypto_driver_wrappers.data
index a58f083..f1a0bf0 100644
--- a/tests/suites/test_suite_psa_crypto_driver_wrappers.data
+++ b/tests/suites/test_suite_psa_crypto_driver_wrappers.data
@@ -1,3 +1,6 @@
+Built-in key range
+builtin_key_id_stability:
+
 sign_hash transparent driver: in driver ECDSA SECP256R1 SHA-256
 depends_on:PSA_WANT_ALG_DETERMINISTIC_ECDSA:PSA_WANT_KEY_TYPE_ECC_KEY_PAIR:PSA_WANT_ECC_SECP_R1_256:PSA_WANT_ALG_SHA_256
 sign_hash:PSA_KEY_TYPE_ECC_KEY_PAIR( PSA_ECC_FAMILY_SECP_R1 ):PSA_ALG_DETERMINISTIC_ECDSA( PSA_ALG_SHA_256 ):PSA_SUCCESS:"ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3a":"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"6a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f":0:PSA_SUCCESS
diff --git a/tests/suites/test_suite_psa_crypto_driver_wrappers.function b/tests/suites/test_suite_psa_crypto_driver_wrappers.function
index eba637f..709fe4f 100644
--- a/tests/suites/test_suite_psa_crypto_driver_wrappers.function
+++ b/tests/suites/test_suite_psa_crypto_driver_wrappers.function
@@ -8,6 +8,21 @@
  */
 
 /* BEGIN_CASE */
+void builtin_key_id_stability()
+{
+    /* If the range of built-in keys is reduced, it's an API break, since
+     * it breaks user code that hard-codes the key id of built-in keys.
+     * It's ok to expand this range, but not to shrink it. That is, you
+     * may make the MIN smaller or the MAX larger at any time, but
+     * making the MIN larger or the MAX smaller can only be done in
+     * a new major version of the library.
+     */
+    TEST_EQUAL(MBEDTLS_PSA_KEY_ID_BUILTIN_MIN, 0x7fff0000);
+    TEST_EQUAL(MBEDTLS_PSA_KEY_ID_BUILTIN_MAX, 0x7fffefff);
+}
+/* END_CASE */
+
+/* BEGIN_CASE */
 void sign_hash(int key_type_arg,
                int alg_arg,
                int force_status_arg,
diff --git a/tests/suites/test_suite_psa_crypto_init.function b/tests/suites/test_suite_psa_crypto_init.function
index 63767f0..eb6bb1a 100644
--- a/tests/suites/test_suite_psa_crypto_init.function
+++ b/tests/suites/test_suite_psa_crypto_init.function
@@ -161,6 +161,8 @@
         PSA_ASSERT(status);
         PSA_DONE();
     }
+exit:
+    PSA_DONE();
 }
 /* END_CASE */
 
diff --git a/tests/suites/test_suite_psa_crypto_se_driver_hal.data b/tests/suites/test_suite_psa_crypto_se_driver_hal.data
index 2bcf4e4..dbe22b8 100644
--- a/tests/suites/test_suite_psa_crypto_se_driver_hal.data
+++ b/tests/suites/test_suite_psa_crypto_se_driver_hal.data
@@ -147,7 +147,16 @@
 Key registration: smoke test
 register_key_smoke_test:TEST_SE_PERSISTENT_LIFETIME:7:1:1:PSA_SUCCESS
 
-Key registration: invalid lifetime (volatile internal storage)
+Key registration: invalid lifetime (volatile, in SE, id=0)
+register_key_smoke_test:TEST_SE_VOLATILE_LIFETIME:7:0:0:PSA_ERROR_INVALID_ARGUMENT
+
+Key registration: invalid lifetime (volatile, in SE, id=1)
+register_key_smoke_test:TEST_SE_VOLATILE_LIFETIME:7:1:1:PSA_ERROR_INVALID_ARGUMENT
+
+Key registration: invalid lifetime (volatile, internal, id=0)
+register_key_smoke_test:PSA_KEY_LIFETIME_VOLATILE:7:0:0:PSA_ERROR_INVALID_ARGUMENT
+
+Key registration: invalid lifetime (volatile, internal, id=1)
 register_key_smoke_test:PSA_KEY_LIFETIME_VOLATILE:7:1:1:PSA_ERROR_INVALID_ARGUMENT
 
 Key registration: invalid lifetime (internal storage)
diff --git a/tests/suites/test_suite_psa_crypto_slot_management.data b/tests/suites/test_suite_psa_crypto_slot_management.data
index 1477734..a731044 100644
--- a/tests/suites/test_suite_psa_crypto_slot_management.data
+++ b/tests/suites/test_suite_psa_crypto_slot_management.data
@@ -214,8 +214,23 @@
 invalid handle: huge
 invalid_handle:INVALID_HANDLE_HUGE:PSA_ERROR_INVALID_HANDLE
 
-Open many transient keys
-many_transient_keys:42
+Key slot count: less than maximum
+many_transient_keys:MBEDTLS_PSA_KEY_SLOT_COUNT - 1
+
+Key slot count: maximum
+many_transient_keys:MBEDTLS_PSA_KEY_SLOT_COUNT
+
+Key slot count: try to overfill, destroy first
+fill_key_store:0
+
+Key slot count: try to overfill, destroy second
+fill_key_store:1
+
+Key slot count: try to overfill, destroy next-to-last
+fill_key_store:-2
+
+Key slot count: try to overfill, destroy last
+fill_key_store:-1
 
 # Eviction from a key slot to be able to import a new persistent key.
 Key slot eviction to import a new persistent key
diff --git a/tests/suites/test_suite_psa_crypto_slot_management.function b/tests/suites/test_suite_psa_crypto_slot_management.function
index 5bd12eb..ee214ea 100644
--- a/tests/suites/test_suite_psa_crypto_slot_management.function
+++ b/tests/suites/test_suite_psa_crypto_slot_management.function
@@ -98,6 +98,11 @@
     return 0;
 }
 
+/* Currently, there is always a maximum number of volatile keys that can
+ * realistically be reached in tests. When we add configurations where this
+ * is not true, undefine the macro in such configurations. */
+#define MAX_VOLATILE_KEYS MBEDTLS_PSA_KEY_SLOT_COUNT
+
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -821,21 +826,19 @@
     psa_set_key_type(&attributes, PSA_KEY_TYPE_RAW_DATA);
 
     for (i = 0; i < max_keys; i++) {
+        mbedtls_test_set_step(i);
         status = psa_import_key(&attributes,
                                 (uint8_t *) &i, sizeof(i),
                                 &keys[i]);
-        if (status == PSA_ERROR_INSUFFICIENT_MEMORY) {
-            break;
-        }
         PSA_ASSERT(status);
         TEST_ASSERT(!mbedtls_svc_key_id_is_null(keys[i]));
         for (j = 0; j < i; j++) {
             TEST_ASSERT(!mbedtls_svc_key_id_equal(keys[i], keys[j]));
         }
     }
-    max_keys = i;
 
     for (i = 1; i < max_keys; i++) {
+        mbedtls_test_set_step(i);
         PSA_ASSERT(psa_close_key(keys[i - 1]));
         PSA_ASSERT(psa_export_key(keys[i],
                                   exported, sizeof(exported),
@@ -851,6 +854,112 @@
 }
 /* END_CASE */
 
+/* BEGIN_CASE depends_on:MAX_VOLATILE_KEYS */
+/*
+ * 1. Fill the key store with volatile keys.
+ * 2. Check that attempting to create another volatile key fails without
+ *    corrupting the key store.
+ * 3. Destroy the key specified by key_to_destroy. This is the number of the
+ *    key in creation order (e.g. 0 means the first key that was created).
+ *    It can also  be a negative value to count in reverse order (e.g.
+ *    -1 means to destroy the last key that was created).
+ * 4. Check that creating another volatile key succeeds.
+ */
+void fill_key_store(int key_to_destroy_arg)
+{
+    mbedtls_svc_key_id_t *keys = NULL;
+    size_t max_keys = MAX_VOLATILE_KEYS;
+    size_t i, j;
+    psa_status_t status;
+    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
+    uint8_t exported[sizeof(size_t)];
+    size_t exported_length;
+
+    PSA_ASSERT(psa_crypto_init());
+
+    mbedtls_psa_stats_t stats;
+    mbedtls_psa_get_stats(&stats);
+    /* Account for any system-created volatile key, e.g. for the RNG. */
+    max_keys -= stats.volatile_slots;
+    TEST_CALLOC(keys, max_keys + 1);
+
+    psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_EXPORT);
+    psa_set_key_algorithm(&attributes, 0);
+    psa_set_key_type(&attributes, PSA_KEY_TYPE_RAW_DATA);
+
+    /* Fill the key store. */
+    for (i = 0; i < max_keys; i++) {
+        mbedtls_test_set_step(i);
+        status = psa_import_key(&attributes,
+                                (uint8_t *) &i, sizeof(i),
+                                &keys[i]);
+        PSA_ASSERT(status);
+        TEST_ASSERT(!mbedtls_svc_key_id_is_null(keys[i]));
+        for (j = 0; j < i; j++) {
+            TEST_ASSERT(!mbedtls_svc_key_id_equal(keys[i], keys[j]));
+        }
+    }
+
+    /* Attempt to overfill. */
+    mbedtls_test_set_step(max_keys);
+    status = psa_import_key(&attributes,
+                            (uint8_t *) &max_keys, sizeof(max_keys),
+                            &keys[max_keys]);
+    TEST_EQUAL(status, PSA_ERROR_INSUFFICIENT_MEMORY);
+    TEST_ASSERT(mbedtls_svc_key_id_is_null(keys[max_keys]));
+
+    /* Check that the keys are not corrupted. */
+    for (i = 0; i < max_keys; i++) {
+        mbedtls_test_set_step(i);
+        PSA_ASSERT(psa_export_key(keys[i],
+                                  exported, sizeof(exported),
+                                  &exported_length));
+        TEST_MEMORY_COMPARE(exported, exported_length,
+                            (uint8_t *) &i, sizeof(i));
+    }
+
+    /* Destroy one key and try again. */
+    size_t key_to_destroy = (key_to_destroy_arg >= 0 ?
+                             (size_t) key_to_destroy_arg :
+                             max_keys + key_to_destroy_arg);
+    mbedtls_svc_key_id_t reused_id = keys[key_to_destroy];
+    const uint8_t replacement_value[1] = { 0x64 };
+    PSA_ASSERT(psa_destroy_key(keys[key_to_destroy]));
+    keys[key_to_destroy] = MBEDTLS_SVC_KEY_ID_INIT;
+    status = psa_import_key(&attributes,
+                            replacement_value, sizeof(replacement_value),
+                            &keys[key_to_destroy]);
+    PSA_ASSERT(status);
+    /* Since the key store was full except for one key, the new key must be
+     * in the same slot in the key store as the destroyed key.
+     * Since volatile keys IDs are assigned based on which slot contains
+     * the key, the new key should have the same ID as the destroyed key.
+     */
+    TEST_ASSERT(mbedtls_svc_key_id_equal(reused_id, keys[key_to_destroy]));
+
+    /* Check that the keys are not corrupted and destroy them. */
+    for (i = 0; i < max_keys; i++) {
+        mbedtls_test_set_step(i);
+        PSA_ASSERT(psa_export_key(keys[i],
+                                  exported, sizeof(exported),
+                                  &exported_length));
+        if (i == key_to_destroy) {
+            TEST_MEMORY_COMPARE(exported, exported_length,
+                                replacement_value, sizeof(replacement_value));
+        } else {
+            TEST_MEMORY_COMPARE(exported, exported_length,
+                                (uint8_t *) &i, sizeof(i));
+        }
+        PSA_ASSERT(psa_destroy_key(keys[i]));
+        keys[i] = MBEDTLS_SVC_KEY_ID_INIT;
+    }
+
+exit:
+    PSA_DONE();
+    mbedtls_free(keys);
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_STORAGE_C */
 void key_slot_eviction_to_import_new_key(int lifetime_arg)
 {