diff --git a/includes/commerce.controller.inc b/includes/commerce.controller.inc
index 1cdd605..30de2d6 100644
--- a/includes/commerce.controller.inc
+++ b/includes/commerce.controller.inc
@@ -21,14 +21,65 @@ class DrupalCommerceEntityController extends DrupalDefaultEntityController imple
   protected $lockedEntities = array();
 
   /**
+   * Determines whether the provided entity is locked.
+   *
+   * @param $entity
+   *   The entity to check.
+   */
+  public function isLocked($entity) {
+    return isset($this->lockedEntities[$entity->{$this->idKey}]);
+  }
+
+  /**
+   * Determines whether the current entity type requires pessimistic locking.
+   */
+  protected function requiresLocking() {
+    return isset($this->entityInfo['locking mode']) && $this->entityInfo['locking mode'] == 'pessimistic';
+  }
+
+  /**
+   * Checks the list of tracked locked entities, and if it's empty, commits
+   * the transaction in order to remove the acquired locks.
+   *
+   * The transaction is not necessarily committed immediately. Drupal will
+   * commit it as soon as possible given the state of the transaction stack.
+   */
+  protected function releaseLock() {
+    if ($this->requiresLocking() && empty($this->lockedEntities)) {
+      unset($this->controllerTransaction);
+    }
+  }
+
+  /**
+   * Overrides DrupalDefaultEntityController::load().
+   */
+  public function load($ids = array(), $conditions = array()) {
+    // If locking has been required, then bypass the internal cache for any
+    // entities that are not already locked.
+    if (!empty($conditions['_lock']) && $this->requiresLocking()) {
+      foreach (array_diff($ids, $this->lockedEntities) as $id) {
+        unset($this->entityCache[$id]);
+      }
+    }
+    elseif (isset($conditions['_lock']) && !$conditions['_lock']) {
+      // Remove the pseudo-condition _lock if it is FALSE.
+      unset($conditions['_lock']);
+    }
+    return parent::load($ids, $conditions);
+  }
+
+  /**
    * Override of DrupalDefaultEntityController::buildQuery().
    *
    * Handle pessimistic locking.
    */
   protected function buildQuery($ids, $conditions = array(), $revision_id = FALSE) {
+    $lock = !empty($conditions['_lock']);
+    unset($conditions['_lock']);
+
     $query = parent::buildQuery($ids, $conditions, $revision_id);
 
-    if (isset($this->entityInfo['locking mode']) && $this->entityInfo['locking mode'] == 'pessimistic') {
+    if ($lock && $this->requiresLocking()) {
       // In pessimistic locking mode, we issue the load query with a FOR UPDATE
       // clause. This will block all other load queries to the loaded objects
       // but requires us to start a transaction.
@@ -48,41 +99,6 @@ class DrupalCommerceEntityController extends DrupalDefaultEntityController imple
     return $query;
   }
 
-  public function resetCache(array $ids = NULL) {
-    parent::resetCache($ids);
-
-    // Maintain the list of locked entities, so that the releaseLock() method
-    // can know when it's time to commit the transaction.
-    if (!empty($this->lockedEntities)) {
-      if (isset($ids)) {
-        foreach ($ids as $id) {
-          unset($this->lockedEntities[$id]);
-        }
-      }
-      else {
-        $this->lockedEntities = array();
-      }
-    }
-
-    // Try to release the lock, if possible.
-    $this->releaseLock();
-  }
-
-  /**
-   * Checks the list of tracked locked entities, and if it's empty, commits
-   * the transaction in order to remove the acquired locks.
-   *
-   * The transaction is not necessarily committed immediately. Drupal will
-   * commit it as soon as possible given the state of the transaction stack.
-   */
-  protected function releaseLock() {
-    if (isset($this->entityInfo['locking mode']) && $this->entityInfo['locking mode'] == 'pessimistic') {
-      if (empty($this->lockedEntities)) {
-        unset($this->controllerTransaction);
-      }
-    }
-  }
-
   /**
    * (Internal use) Invokes a hook on behalf of the entity.
    *
@@ -124,6 +140,24 @@ class DrupalCommerceEntityController extends DrupalDefaultEntityController imple
       return;
     }
 
+    if ($this->requiresLocking()) {
+      // Forbid the deletion of unlocked entities.
+      foreach ($entities as $entity) {
+        $unlocked_entities = array();
+        if (!isset($this->lockedEntities[$entity->{$this->idKey}])) {
+          $unlocked_ids[] = $entity->{$this->idKey};
+        }
+
+        if ($unlocked_ids) {
+          $args = array(
+            '@entity_type' => $this->entityType,
+            '@ids' => implode(', ', $unlocked_ids),
+          );
+          throw new Exception(format_string('Cannot delete unlocked @entity_type entities: @ids.', $args));
+        }
+      }
+    }
+
     if (!isset($transaction)) {
       $transaction = db_transaction();
       $started_transaction = TRUE;
@@ -173,6 +207,22 @@ class DrupalCommerceEntityController extends DrupalDefaultEntityController imple
    *   SAVED_NEW or SAVED_UPDATED depending on the operation performed.
    */
   public function save($entity, DatabaseTransaction $transaction = NULL) {
+    if ($this->requiresLocking()) {
+      // Forbid the saving of unlocked entities.
+      if (!empty($entity->{$this->idKey}) && !$this->isLocked($entity)) {
+        $args = array(
+          '@entity_type' => $this->entityType,
+          '@id' => $entity->{$this->idKey},
+        );
+        // Debug locking issues.
+        // @todo remove this when #2240427 is finally solved
+        if (function_exists('dpm')) {
+          dpm(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 6));
+        }
+        throw new Exception(format_string('Cannot save unlocked @entity_type entity #@id', $args));
+      }
+    }
+
     if (!isset($transaction)) {
       $transaction = db_transaction();
       $started_transaction = TRUE;
@@ -237,9 +287,11 @@ class DrupalCommerceEntityController extends DrupalDefaultEntityController imple
       // newly saved entity.
       $this->entityCache[$entity->{$this->idKey}] = $entity;
 
-      // Maintain the list of locked entities and release the lock if possible.
-      unset($this->lockedEntities[$entity->{$this->idKey}]);
-      $this->releaseLock();
+      if ($this->requiresLocking()) {
+        // Maintain the list of locked entities and release the lock if possible.
+        unset($this->lockedEntities[$entity->{$this->idKey}]);
+        $this->releaseLock();
+      }
 
       $this->invoke($op, $entity);
 
diff --git a/modules/cart/commerce_cart.module b/modules/cart/commerce_cart.module
index ced58af..25974ec 100644
--- a/modules/cart/commerce_cart.module
+++ b/modules/cart/commerce_cart.module
@@ -50,6 +50,8 @@ function commerce_cart_menu() {
   // their own local action menu items if needed.
   if (module_exists('commerce_order_ui')) {
     $items['admin/commerce/orders/%commerce_order/edit/refresh'] = array(
+      // Lock the loaded order.
+      'load arguments' => array(TRUE),
       'title' => 'Apply pricing rules',
       'description' => 'Executes the cart order refresh used to apply all current pricing rules on the front end.',
       'page callback' => 'drupal_get_form',
@@ -286,7 +288,7 @@ function commerce_cart_form_alter(&$form, &$form_state, $form_id) {
  */
 function commerce_cart_checkout_form_cancel_submit($form, &$form_state) {
   // Update the order to the cart status.
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
   $form_state['order'] = commerce_order_status_update($order, 'cart', TRUE);
 
   // Skip saving in the status update and manually save here to force a save
@@ -309,7 +311,7 @@ function commerce_cart_checkout_form_cancel_submit($form, &$form_state) {
  */
 function commerce_cart_line_item_views_form_submit($form, &$form_state) {
   // Reset the status of the order to cart.
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
   $form_state['order'] = commerce_order_status_update($order, 'cart', TRUE);
 
   // Skip saving in the status update and manually save here to force a save
@@ -590,7 +592,7 @@ function commerce_cart_theme() {
  */
 function commerce_cart_user_login(&$edit, $account) {
   // Get the user's anonymous shopping cart order if it exists.
-  if ($order = commerce_cart_order_load()) {
+  if ($order = commerce_cart_order_load($account->uid, TRUE)) {
     // Convert it to an authenticated cart.
     commerce_cart_order_convert($order, $account);
   }
@@ -616,7 +618,7 @@ function commerce_cart_user_update(&$edit, $account, $category) {
     $result = $query->execute();
 
     if (!empty($result['commerce_order'])) {
-      foreach (commerce_order_load_multiple(array_keys($result['commerce_order'])) as $order) {
+      foreach (commerce_order_load_multiple(array_keys($result['commerce_order']), array(), FALSE, TRUE, TRUE) as $order) {
         if ($order->mail != $account->mail) {
           $order->mail = $account->mail;
           commerce_order_save($order);
@@ -688,6 +690,11 @@ function commerce_cart_block_view($delta) {
 function commerce_cart_order_can_refresh($order) {
   global $user;
 
+  // Unlocked orders can't be modified.
+  if (!commerce_order_is_locked($order)) {
+    return FALSE;
+  }
+
   // Force the shopping cart refresh on /cart and /checkout/* paths if enabled.
   if (variable_get('commerce_cart_refresh_force', TRUE) &&
     (current_path() == 'cart' || strpos(current_path(), 'checkout/') === 0)) {
@@ -797,20 +804,27 @@ function theme_commerce_cart_empty_page() {
 /**
  * Loads the shopping cart order for the specified user.
  *
+ * By default, the returned order is unlocked and can only be used for
+ * reading purposes. Orders meant to be saved or deleted must be locked,
+ * which means all other attempts to load the same order will be blocked
+ * until the order is saved or deleted.
+ *
  * @param $uid
  *   The uid of the customer whose cart to load. If left 0, attempts to load
  *   an anonymous order from the session.
+ * @param $lock
+ *   Whether to lock the loaded order.
  *
  * @return
  *   The fully loaded shopping cart order or FALSE if nonexistent.
  */
-function commerce_cart_order_load($uid = 0) {
+function commerce_cart_order_load($uid = 0, $lock = FALSE) {
   // Retrieve the order ID for the specified user's current shopping cart.
   $order_id = commerce_cart_order_id($uid);
 
   // If a valid cart order ID exists for the user, return it now.
   if (!empty($order_id)) {
-    return commerce_order_load($order_id);
+    return commerce_order_load($order_id, $lock);
   }
 
   return FALSE;
@@ -1003,7 +1017,8 @@ function commerce_cart_commerce_entity_access_condition_commerce_order_alter(&$c
  * Converts an anonymous shopping cart order to an authenticated cart.
  *
  * @param $order
- *   The anonymous order to convert to an authenticated cart.
+ *   The anonymous order to convert to an authenticated cart. The order must be
+ *   locked (see commerce_order_load()).
  * @param $account
  *   The user account the order will belong to.
  *
@@ -1298,11 +1313,13 @@ function commerce_cart_product_add($uid, $line_item, $combine = TRUE) {
   }
 
   // First attempt to load the customer's shopping cart order.
-  $order = commerce_cart_order_load($uid);
+  $order = commerce_cart_order_load($uid, TRUE);
 
   // If no order existed, create one now.
   if (empty($order)) {
     $order = commerce_cart_order_new($uid);
+    // Reload the order from the database, to enable locking.
+    $order = commerce_order_load($order->order_id, TRUE);
     $order->data['last_cart_refresh'] = REQUEST_TIME;
   }
 
@@ -1453,16 +1470,12 @@ function commerce_cart_product_add_by_id($product_id, $quantity = 1, $combine =
  *   The shopping cart order to delete from.
  * @param $line_item_id
  *   The ID of the product line item to delete from the order.
- * @param $skip_save
- *   TRUE to skip saving the order after deleting the line item; used when the
- *     order would otherwise be saved or to delete multiple product line items
- *     from the order and then save.
  *
  * @return
  *   The order with the matching product line item deleted from the line item
  *     reference field.
  */
-function commerce_cart_order_product_line_item_delete($order, $line_item_id, $skip_save = FALSE) {
+function commerce_cart_order_product_line_item_delete($order, $line_item_id) {
   $line_item = commerce_line_item_load($line_item_id);
 
   // Check to ensure the line item exists and is a product line item.
@@ -1480,13 +1493,10 @@ function commerce_cart_order_product_line_item_delete($order, $line_item_id, $sk
   // Invoke the product removal event with the line item about to be deleted.
   rules_invoke_all('commerce_cart_product_remove', $order, $product, $line_item->quantity, $line_item);
 
-  // Delete the actual line item.
+  // Delete the actual line item. This will in turn save the order, because the
+  // reference will be deleted.
   commerce_line_item_delete($line_item->line_item_id);
 
-  if (!$skip_save) {
-    commerce_order_save($order);
-  }
-
   return $order;
 }
 
diff --git a/modules/cart/includes/commerce_cart.admin.inc b/modules/cart/includes/commerce_cart.admin.inc
index bccf451..88d069c 100644
--- a/modules/cart/includes/commerce_cart.admin.inc
+++ b/modules/cart/includes/commerce_cart.admin.inc
@@ -45,7 +45,7 @@ function commerce_cart_order_refresh_form($form, &$form_state, $order) {
  * Form submit callback for commerce_cart_order_refresh_form().
  */
 function commerce_cart_order_refresh_form_submit($form, &$form_state) {
-  if ($order = commerce_order_load($form_state['values']['order_id'])) {
+  if ($order = commerce_order_load($form_state['values']['order_id'], TRUE)) {
     commerce_cart_order_refresh($order);
     drupal_set_message(t('Pricing rules have been applied and the order updated.'));
     $form_state['redirect'] = 'admin/commerce/orders/' . $order->order_id . '/edit';
diff --git a/modules/cart/tests/commerce_cart.test b/modules/cart/tests/commerce_cart.test
index 723fa1f..ddc559c 100644
--- a/modules/cart/tests/commerce_cart.test
+++ b/modules/cart/tests/commerce_cart.test
@@ -510,8 +510,6 @@ class CommerceCartTestCaseAnonymousToAuthenticated extends CommerceCartTestCase
 
     // Get the order just created.
     $order_anonymous = reset(commerce_order_load_multiple(array(), array('uid' => $user->uid, 'status' => 'cart'), TRUE));
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
 
     // Access to the cart and check if the product is in it.
     $this->drupalGet($this->getCommerceUrl('cart'));
@@ -530,8 +528,6 @@ class CommerceCartTestCaseAnonymousToAuthenticated extends CommerceCartTestCase
 
     // Get the order for user just logged in.
     $order_authenticated = reset(commerce_order_load_multiple(array(), array('uid' => $this->store_customer->uid, 'status' => 'cart'), TRUE));
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
 
     // Access to the cart and check if the product is in it.
     $this->drupalGet($this->getCommerceUrl('cart'));
diff --git a/modules/checkout/commerce_checkout.module b/modules/checkout/commerce_checkout.module
index 1f390fa..bd41fa9 100644
--- a/modules/checkout/commerce_checkout.module
+++ b/modules/checkout/commerce_checkout.module
@@ -87,6 +87,8 @@ function commerce_checkout_menu() {
   // defining their own local action menu items if needed.
   if (module_exists('commerce_order_ui')) {
     $items['admin/commerce/orders/%commerce_order/edit/checkout'] = array(
+      // Lock the loaded order.
+      'load arguments' => array(TRUE),
       'title' => 'Simulate checkout completion',
       'description' => 'Directly invokes the checkout completion rules on the order.',
       'page callback' => 'drupal_get_form',
@@ -263,7 +265,7 @@ function commerce_checkout_form_alter(&$form, &$form_state, $form_id) {
  * Submit handler used to redirect to the checkout page.
  */
 function commerce_checkout_line_item_views_form_submit($form, &$form_state) {
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
 
   // Set the order status to the first checkout page's status.
   $order_state = commerce_order_state_load('checkout');
@@ -936,6 +938,7 @@ function commerce_checkout_order_can_checkout($order) {
  * Completes the checkout process for the given order.
  */
 function commerce_checkout_complete($order) {
+  $order = commerce_order_load($order->order_id, TRUE);
   rules_invoke_all('commerce_checkout_complete', $order);
 }
 
diff --git a/modules/checkout/includes/commerce_checkout.admin.inc b/modules/checkout/includes/commerce_checkout.admin.inc
index 3c17859..925f9ea 100644
--- a/modules/checkout/includes/commerce_checkout.admin.inc
+++ b/modules/checkout/includes/commerce_checkout.admin.inc
@@ -438,7 +438,7 @@ function commerce_checkout_complete_form($form, &$form_state, $order) {
  * Form submit callback for commerce_checkout_complete_form().
  */
 function commerce_checkout_complete_form_submit($form, &$form_state) {
-  if ($order = commerce_order_load($form_state['values']['order_id'])) {
+  if ($order = commerce_order_load($form_state['values']['order_id'], TRUE)) {
     commerce_checkout_complete($order);
     drupal_set_message(t('Checkout completion rules have been executed for the order.'));
     $form_state['redirect'] = 'admin/commerce/orders/' . $order->order_id . '/edit';
diff --git a/modules/checkout/includes/commerce_checkout.pages.inc b/modules/checkout/includes/commerce_checkout.pages.inc
index 6bbd013..a22fafe 100644
--- a/modules/checkout/includes/commerce_checkout.pages.inc
+++ b/modules/checkout/includes/commerce_checkout.pages.inc
@@ -232,7 +232,7 @@ function commerce_checkout_form_validate($form, &$form_state) {
   $checkout_page = $form_state['checkout_page'];
 
   // Load a fresh copy of the order stored in the form.
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
 
   // Catch and clear already pushed messages.
   $previous_messages = drupal_get_messages();
@@ -295,6 +295,7 @@ function commerce_checkout_form_validate($form, &$form_state) {
 
   // Save the updated order object and reset the order in the form cache to
   // ensure rebuilt forms use the updated order.
+  $order = commerce_order_load($order->order_id, TRUE);
   commerce_order_save($order);
   $form_state['build_info']['args'][0] = $order;
 
@@ -312,7 +313,7 @@ function commerce_checkout_form_submit($form, &$form_state) {
   $checkout_page = $form_state['checkout_page'];
 
   // Load a fresh copy of the order stored in the form.
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
 
   // If we are going to redirect with checkout pane messages stored in the form
   // state, they will not be displayed on a subsequent form build like normal.
@@ -348,7 +349,7 @@ function commerce_checkout_form_submit($form, &$form_state) {
 function commerce_checkout_form_back_submit($form, &$form_state) {
   // If there is a previous page...
   if ($previous_page = commerce_checkout_page_load($form_state['checkout_page']['prev_page'])) {
-    $order = commerce_order_load($form_state['order']->order_id);
+    $order = commerce_order_load($form_state['order']->order_id, TRUE);
 
     // Move the form back to that page.
     if ($previous_page['prev_page']) {
@@ -367,7 +368,7 @@ function commerce_checkout_form_back_submit($form, &$form_state) {
  * Special submit handler for the cancel button to avoid processing orders.
  */
 function commerce_checkout_form_cancel_submit($form, &$form_state) {
-  $order = commerce_order_load($form_state['order']->order_id);
+  $order = commerce_order_load($form_state['order']->order_id, TRUE);
 
   // Set the order status back to the first checkout page's status.
   $order_state = commerce_order_state_load('checkout');
diff --git a/modules/checkout/tests/commerce_checkout.test b/modules/checkout/tests/commerce_checkout.test
index 20a99a2..ff0fbd9 100644
--- a/modules/checkout/tests/commerce_checkout.test
+++ b/modules/checkout/tests/commerce_checkout.test
@@ -68,7 +68,7 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
     // Logout to test the checkout process with anonymous user.
     $this->drupalLogout();
 
-    // Override user variable to get the enviroment fully set.
+    // Override user variable to get the environment fully set.
     global $user;
     $user = user_load(0);
 
@@ -76,9 +76,7 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
     $this->drupalPost('node/' . $this->product_node->nid, array(), t('Add to cart'));
 
     // Get the order for the anonymous user.
-    $this->order = reset(commerce_order_load_multiple(array(), array('uid' => $user->uid, 'status' => 'cart'), TRUE));
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
+    $this->order = reset(commerce_order_load_multiple(array(), array('uid' => $user->uid, 'status' => 'cart'), TRUE, TRUE));
   }
 
   /**
@@ -162,8 +160,6 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
 
     // Load the order to check the status.
     $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
 
     // At this point we should be in Checkout Review.
     $this->assertEqual(reset($order)->status, 'checkout_review', t('Order status is \'Checkout Review\' in the review phase.'));
@@ -178,7 +174,7 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
     $this->drupalPost(NULL, array(), t('Continue to next step'));
 
     // Reload the order directly from db to update status.
-    $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
+    $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE, TRUE);
 
     // Order status should be pending when completing checkout process.
     $this->assertEqual(reset($order)->status, 'pending', t('Order status is \'Pending\' after completing checkout'));
@@ -324,8 +320,6 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
 
     // Load the order to check the status.
     $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
 
     // At this point we should be in Checkout Review.
     $this->assertEqual(reset($order)->status, 'checkout_review', t('Order status is \'Checkout Review\' in the review phase.'));
@@ -334,7 +328,7 @@ class CommerceCheckoutTestProcess extends CommerceBaseTestCase {
     $this->drupalPost(NULL, array(), t('Continue to next step'));
 
     // Reload the order directly from db to check status.
-    $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
+    $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE, TRUE);
 
     // Order status should be pending when completing checkout process.
     $this->assertEqual(reset($order)->status, 'pending', t('Order status is \'Pending\' after completing checkout.'));
diff --git a/modules/customer/commerce_customer.module b/modules/customer/commerce_customer.module
index 649ff2a..6231219 100644
--- a/modules/customer/commerce_customer.module
+++ b/modules/customer/commerce_customer.module
@@ -740,7 +740,7 @@ function commerce_customer_commerce_customer_profile_delete($profile) {
       // Loop over results for each type of entity returned.
       foreach ($result as $entity_type => $data) {
         // Load the entities of the current type.
-        $entities = entity_load($entity_type, array_keys($data));
+        $entities = entity_load($entity_type, array_keys($data), array('_lock' => TRUE));
 
         // Loop over each entity and remove the reference to the deleted profile.
         foreach ($entities as $entity_id => $entity) {
diff --git a/modules/line_item/commerce_line_item.module b/modules/line_item/commerce_line_item.module
index b5eee98..47211e3 100644
--- a/modules/line_item/commerce_line_item.module
+++ b/modules/line_item/commerce_line_item.module
@@ -656,7 +656,7 @@ function commerce_line_item_delete_references($line_item) {
       // Loop over results for each type of entity returned.
       foreach ($result as $entity_type => $data) {
         // Load the entities of the current type.
-        $entities = entity_load($entity_type, array_keys($data));
+        $entities = entity_load($entity_type, array_keys($data), array('_lock'=> TRUE));
 
         // Loop over each entity and remove the reference to the deleted line item.
         foreach ($entities as $entity_id => $entity) {
diff --git a/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_delete.inc b/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_delete.inc
index ccd4b0e..cbe3da8 100644
--- a/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_delete.inc
+++ b/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_delete.inc
@@ -53,7 +53,7 @@ class commerce_line_item_handler_field_edit_delete extends views_handler_field {
   }
 
   function views_form_submit($form, &$form_state) {
-    $order = commerce_order_load($form_state['order']->order_id);
+    $order = commerce_order_load($form_state['order']->order_id, TRUE);
     $field_name = $this->options['id'];
 
     foreach (element_children($form[$field_name]) as $row_id) {
diff --git a/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_quantity.inc b/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_quantity.inc
index be9fe55..c078527 100644
--- a/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_quantity.inc
+++ b/modules/line_item/includes/views/handlers/commerce_line_item_handler_field_edit_quantity.inc
@@ -102,7 +102,7 @@ class commerce_line_item_handler_field_edit_quantity extends views_handler_field
 
     // Process the deletes first.
     foreach ($deleted_line_items as $line_item_id) {
-      $order = commerce_order_load($form_state['order']->order_id);
+      $order = commerce_order_load($form_state['order']->order_id, TRUE);
       commerce_cart_order_product_line_item_delete($order, $line_item_id);
     }
 
diff --git a/modules/order/commerce_order.install b/modules/order/commerce_order.install
index 4aa42ec..ed14103 100644
--- a/modules/order/commerce_order.install
+++ b/modules/order/commerce_order.install
@@ -340,7 +340,7 @@ function commerce_order_update_7102(&$sandbox) {
 
   // Loop over the orders, loading and resaving each one.
   foreach ($orders as $order) {
-    $order = commerce_order_load($order->order_id);
+    $order = commerce_order_load($order->order_id, TRUE);
 
     // Save the order as a new revision with an update log message.
     $order->revision = TRUE;
diff --git a/modules/order/commerce_order.module b/modules/order/commerce_order.module
index 7bbe0e8..7c54326 100644
--- a/modules/order/commerce_order.module
+++ b/modules/order/commerce_order.module
@@ -746,24 +746,43 @@ function commerce_order_save($order) {
 
 /**
  * Loads an order by ID.
+ *
+ * By default, the returned order is unlocked and can only be used for
+ * reading purposes. Orders meant to be saved or deleted must be locked,
+ * which means all other attempts to load the same order will be blocked
+ * until the order is saved or deleted.
+ *
+ * @param $lock
+ *   Whether to lock the loaded order.
  */
-function commerce_order_load($order_id) {
-  $orders = commerce_order_load_multiple(array($order_id), array());
+function commerce_order_load($order_id, $lock = FALSE) {
+  $orders = commerce_order_load_multiple(array($order_id), array(), FALSE, $lock);
   return $orders ? reset($orders) : FALSE;
 }
 
 /**
  * Loads an order by number.
+ *
+ * By default, the returned order is unlocked and can only be used for
+ * reading purposes. Orders meant to be saved or deleted must be locked,
+ * which means all other attempts to load the same order will be blocked
+ * until the order is saved or deleted.
+ *
+ * @param $lock
+ *   Whether to lock the loaded order.
  */
-function commerce_order_load_by_number($order_number) {
-  $orders = commerce_order_load_multiple(array(), array('order_number' => $order_number));
+function commerce_order_load_by_number($order_number, $lock = FALSE) {
+  $orders = commerce_order_load_multiple(array(), array('order_number' => $order_number), FALSE, $lock);
   return $orders ? reset($orders) : FALSE;
 }
 
 /**
  * Loads multiple orders by ID or based on a set of matching conditions.
  *
- * @see entity_load()
+ * By default, the returned orders are unlocked and can only be used for
+ * reading purposes. Orders meant to be saved or deleted must be locked,
+ * which means all other attempts to load the same order will be blocked
+ * until the order is saved or deleted.
  *
  * @param $order_ids
  *   An array of order IDs.
@@ -774,15 +793,31 @@ function commerce_order_load_by_number($order_number) {
  *   the $order_ids array assuming the revision_id is valid for the order_id.
  * @param $reset
  *   Whether to reset the internal order loading cache.
+ * @param $lock
+ *   Whether to lock the loaded order.
  *
  * @return
  *   An array of order objects indexed by order_id.
  */
-function commerce_order_load_multiple($order_ids = array(), $conditions = array(), $reset = FALSE) {
+function commerce_order_load_multiple($order_ids = array(), $conditions = array(), $reset = FALSE, $lock = FALSE) {
+  $conditions['_lock'] = $lock;
   return entity_load('commerce_order', $order_ids, $conditions, $reset);
 }
 
 /**
+ * Determines whether or not the given order object is locked.
+ *
+ * @param $order
+ *   A fully loaded order object.
+ *
+ * @return
+ *   Boolean indicating whether or not the order object is locked.
+ */
+function commerce_order_is_locked($order) {
+  return entity_get_controller('commerce_order')->isLocked($order);
+}
+
+/**
  * Determines whether or not the given order object represents the latest
  * revision of the order.
  *
diff --git a/modules/order/commerce_order_ui.module b/modules/order/commerce_order_ui.module
index 43db91b..47cb739 100644
--- a/modules/order/commerce_order_ui.module
+++ b/modules/order/commerce_order_ui.module
@@ -48,6 +48,8 @@ function commerce_order_ui_menu() {
     'context' => MENU_CONTEXT_PAGE | MENU_CONTEXT_INLINE,
   );
   $items['admin/commerce/orders/%commerce_order/edit'] = array(
+    // Lock the loaded order.
+    'load arguments' => array(TRUE),
     'title' => 'Edit',
     'page callback' => 'commerce_order_ui_order_form_wrapper',
     'page arguments' => array(3),
@@ -59,6 +61,8 @@ function commerce_order_ui_menu() {
     'file' => 'includes/commerce_order_ui.orders.inc',
   );
   $items['admin/commerce/orders/%commerce_order/delete'] = array(
+    // Lock the loaded order.
+    'load arguments' => array(TRUE),
     'title' => 'Delete',
     'page callback' => 'commerce_order_ui_order_delete_form_wrapper',
     'page arguments' => array(3),
diff --git a/modules/order/includes/commerce_order.forms.inc b/modules/order/includes/commerce_order.forms.inc
index 4ed313d..993ce3f 100644
--- a/modules/order/includes/commerce_order.forms.inc
+++ b/modules/order/includes/commerce_order.forms.inc
@@ -219,7 +219,7 @@ function commerce_order_order_form_submit($form, &$form_state) {
 
   // If the user is editing an order, load a fresh copy to merge changes to.
   if ($form_state['commerce_order']->order_id) {
-    $form_state['commerce_order'] = commerce_order_load($form_state['commerce_order']->order_id);
+    $form_state['commerce_order'] = commerce_order_load($form_state['commerce_order']->order_id, TRUE);
   }
 
   // Merge changes into the order object in the form state so it is accessible
diff --git a/modules/order/tests/commerce_order.test b/modules/order/tests/commerce_order.test
index 1164634..b5eec85 100644
--- a/modules/order/tests/commerce_order.test
+++ b/modules/order/tests/commerce_order.test
@@ -45,7 +45,7 @@ class CommerceOrderCRUDTestCase extends CommerceBaseTestCase {
     $this->assertIdentical($return, SAVED_NEW, 'commerce_order_save() successfully saved the new order.');
 
     // Ensure commerce_order_load() loaded the saved order.
-    $loaded_order = commerce_order_load($new_order->order_id);
+    $loaded_order = commerce_order_load($new_order->order_id, TRUE);
     foreach ($fields as $field) {
       $this->assertEqual($loaded_order->{$field}, $new_order->{$field}, 'The ' . check_plain($field) . ' value loaded by commerce_order_load() matches the value saved by commerce_order_save()');
     }
@@ -77,7 +77,7 @@ class CommerceOrderCRUDTestCase extends CommerceBaseTestCase {
       $saved_orders[$order->order_id] = $order->order_number;
     }
 
-    $loaded_orders = commerce_order_load_multiple(array_keys($saved_orders));
+    $loaded_orders = commerce_order_load_multiple(array_keys($saved_orders), array(), TRUE, TRUE);
     $this->assertEqual(count($saved_orders), count($loaded_orders), 'commerce_order_load_multiple() loaded the proper number of the orders.');
     foreach ($loaded_orders as $loaded_order) {
       $this->assertEqual($loaded_order->order_number, $saved_orders[$loaded_order->order_id], 'commerce_order_load_multiple() successfully loaded a order.');
diff --git a/modules/order/tests/commerce_order_ui.test b/modules/order/tests/commerce_order_ui.test
index 969fed6..135e34a 100644
--- a/modules/order/tests/commerce_order_ui.test
+++ b/modules/order/tests/commerce_order_ui.test
@@ -63,9 +63,6 @@ class CommerceOrderUIAdminTest extends CommerceBaseTestCase {
     $orders = commerce_order_load_multiple(array(), array('uid' => $this->store_customer->uid));
     $this->order = reset($orders);
 
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
-
     // Enable an additional currency.
     $this->enableCurrencies(array('EUR'));
   }
@@ -152,9 +149,6 @@ class CommerceOrderUIAdminTest extends CommerceBaseTestCase {
     // Reload the order directly from db.
     $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
 
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
-
     // Check if the product has been added to the order.
     foreach (entity_metadata_wrapper('commerce_order', reset($order))->commerce_line_items as $delta => $line_item_wrapper) {
        if ($line_item_wrapper->type->value() == 'product') {
@@ -190,9 +184,6 @@ class CommerceOrderUIAdminTest extends CommerceBaseTestCase {
     $order = reset($orders);
     $order_wrapper = entity_metadata_wrapper('commerce_order', $order);
 
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
-
     // Also wrap the product to access easier to its price.
     $product_wrapper = entity_metadata_wrapper('commerce_product', $this->product);
 
@@ -264,8 +255,6 @@ class CommerceOrderUIAdminTest extends CommerceBaseTestCase {
 
     // Check if the links for editing the order are present.
     $links = menu_contextual_links('commerce-order', 'admin/commerce/orders', array($this->order->order_id));
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
     $this->assertRaw((theme('links', array('links' => $links, 'attributes' => array('class' => array('links', 'inline', 'operations'))))), t('Links for orders are present'));
 
     $this->drupalGet('admin/commerce/orders/'. $this->order->order_id . '/view');
diff --git a/modules/payment/commerce_payment.module b/modules/payment/commerce_payment.module
index 4b5f166..1503f85 100644
--- a/modules/payment/commerce_payment.module
+++ b/modules/payment/commerce_payment.module
@@ -334,6 +334,11 @@ function commerce_payment_redirect_pane_next_page($order, $log = '') {
   $order_status = commerce_order_status_load($order->status);
 
   if ($order_status['state'] == 'checkout' && $order_status['checkout_page'] == 'payment') {
+    // Reload the order with locking.
+    if (!entity_get_controller('commerce_order')->isLocked($order)) {
+      $order = commerce_order_load($order->order_id, TRUE);
+    }
+
     $payment_page = commerce_checkout_page_load($order_status['checkout_page']);
     $next_page = $payment_page['next_page'];
 
@@ -448,7 +453,7 @@ function commerce_payment_commerce_payment_transaction_insert($transaction) {
   // If the inserted transaction was marked as a success and placed against a
   // valid order...
   if ($transaction->status == COMMERCE_PAYMENT_STATUS_SUCCESS &&
-    $order = commerce_order_load($transaction->order_id)) {
+    $order = commerce_order_load($transaction->order_id, TRUE)) {
     // Then check to make sure the event hasn't been invoked for this order.
     if (empty($order->data['commerce_payment_order_paid_in_full_invoked'])) {
       // Check the order balance and invoke the event.
diff --git a/modules/payment/tests/commerce_payment_ui.test b/modules/payment/tests/commerce_payment_ui.test
index b59e657..1c73dfb 100644
--- a/modules/payment/tests/commerce_payment_ui.test
+++ b/modules/payment/tests/commerce_payment_ui.test
@@ -144,8 +144,6 @@ class CommercePaymentUITest extends CommerceBaseTestCase {
 
     // Reload the order.
     $order = commerce_order_load_multiple(array($this->order->order_id), array(), TRUE);
-    // Reset the cache as we don't want to keep the lock.
-    entity_get_controller('commerce_order')->resetCache();
 
     // Check order balance, it should be half of total now.
     $new_balance = commerce_payment_order_balance(reset($order));
diff --git a/modules/product_reference/commerce_product_reference.module b/modules/product_reference/commerce_product_reference.module
index c9f6ca6..5fe1a1f 100644
--- a/modules/product_reference/commerce_product_reference.module
+++ b/modules/product_reference/commerce_product_reference.module
@@ -289,7 +289,7 @@ function commerce_product_reference_commerce_product_delete($product) {
       // Loop over results for each type of entity returned.
       foreach ($result as $entity_type => $data) {
         // Load the entities of the current type.
-        $entities = entity_load($entity_type, array_keys($data));
+        $entities = entity_load($entity_type, array_keys($data), array('_lock' => TRUE));
 
         // Loop over each entity and remove the reference to the deleted product.
         foreach ($entities as $entity_id => $entity) {
diff --git a/tests/commerce_base.test b/tests/commerce_base.test
index d0c9f00..bbb9032 100644
--- a/tests/commerce_base.test
+++ b/tests/commerce_base.test
@@ -367,12 +367,12 @@ abstract class CommerceBaseTestCase extends DrupalWebTestCase {
     foreach($products as $product_id => $quantity) {
       if ($product = commerce_product_load($product_id)) {
         $line_item = commerce_product_line_item_new($product, $quantity);
-        $line_item = commerce_cart_product_add($uid, $line_item);
+        commerce_cart_product_add($uid, $line_item);
       }
     }
 
     // Load the order for returning it.
-    $order = commerce_cart_order_load($uid);
+    $order = commerce_cart_order_load($uid, TRUE);
 
     if (!empty($customer_profile_id)) {
       $order->commerce_customer_billing[LANGUAGE_NONE][0]['profile_id'] = $customer_profile_id;