diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index e6d3851..c816668 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1071,6 +1071,10 @@
         return status;
     }
 
+#if defined(MBEDTLS_THREADING_C)
+    PSA_THREADING_CHK_GOTO_EXIT(mbedtls_mutex_lock(
+                                    &mbedtls_threading_key_slot_mutex));
+#endif
     /* Set the key slot containing the key description's state to
      * PENDING_DELETION. This stops new operations from registering
      * to read the slot. Current readers can safely continue to access
@@ -1079,7 +1083,12 @@
      * If the key is persistent, we can now delete the copy of the key
      * from memory. If the key is opaque, we require the driver to
      * deal with the deletion. */
-    slot->state = PSA_SLOT_PENDING_DELETION;
+    status = psa_key_slot_state_transition(slot, PSA_SLOT_FULL,
+                                           PSA_SLOT_PENDING_DELETION);
+
+    if (status != PSA_SUCCESS) {
+        goto exit;
+    }
 
     if (PSA_KEY_LIFETIME_IS_READ_ONLY(slot->attr.lifetime)) {
         /* Refuse the destruction of a read-only key (which may or may not work
@@ -1134,11 +1143,6 @@
         if (overall_status == PSA_SUCCESS) {
             overall_status = status;
         }
-
-        /* TODO: other slots may have a copy of the same key. We should
-         * invalidate them.
-         * https://github.com/ARMmbed/mbed-crypto/issues/214
-         */
     }
 #endif /* defined(MBEDTLS_PSA_CRYPTO_STORAGE_C) */
 
@@ -1159,8 +1163,14 @@
     /* Unregister from reading the slot. If we are the last active reader
      * then this will wipe the slot. */
     status = psa_unregister_read(slot);
-    /* Prioritize CORRUPTION_DETECTED from unregistering over
-     * a storage error. */
+
+#if defined(MBEDTLS_THREADING_C)
+    PSA_THREADING_CHK_RET(mbedtls_mutex_unlock(
+                              &mbedtls_threading_key_slot_mutex));
+#endif
+
+    /* Prioritize CORRUPTION_DETECTED from unregistering or
+     * SERVICE_FAILURE from unlocking over a storage error. */
     if (status != PSA_SUCCESS) {
         overall_status = status;
     }