diff --git a/src/wp-admin/nav-menus.php b/src/wp-admin/nav-menus.php
index 28dbc8219f..b14a20fce1 100644
--- a/src/wp-admin/nav-menus.php
+++ b/src/wp-admin/nav-menus.php
@@ -117,6 +117,10 @@ switch ( $action ) {
 						if ( ! is_wp_error( $parent_object ) ) {
 							$parent_data                        = (array) $parent_object;
 							$menu_item_data['menu_item_parent'] = $parent_data['menu_item_parent'];
+
+							// Reset invalid `menu_item_parent`.
+							$menu_item_data = _wp_reset_invalid_menu_item_parent( $menu_item_data );
+
 							update_post_meta( $menu_item_data['ID'], '_menu_item_menu_item_parent', (int) $menu_item_data['menu_item_parent'] );
 						}
 
@@ -126,6 +130,10 @@ switch ( $action ) {
 						$menu_item_data['menu_order'] = $menu_item_data['menu_order'] + 1;
 
 						$menu_item_data['menu_item_parent'] = $next_item_data['ID'];
+
+						// Reset invalid `menu_item_parent`.
+						$menu_item_data = _wp_reset_invalid_menu_item_parent( $menu_item_data );
+
 						update_post_meta( $menu_item_data['ID'], '_menu_item_menu_item_parent', (int) $menu_item_data['menu_item_parent'] );
 
 						wp_update_post( $menu_item_data );
@@ -137,6 +145,10 @@ switch ( $action ) {
 					&& in_array( (int) $menu_item_data['menu_item_parent'], $orders_to_dbids, true )
 				) {
 					$menu_item_data['menu_item_parent'] = (int) get_post_meta( $menu_item_data['menu_item_parent'], '_menu_item_menu_item_parent', true );
+
+					// Reset invalid `menu_item_parent`.
+					$menu_item_data = _wp_reset_invalid_menu_item_parent( $menu_item_data );
+
 					update_post_meta( $menu_item_data['ID'], '_menu_item_menu_item_parent', (int) $menu_item_data['menu_item_parent'] );
 				}
 			}
@@ -247,6 +259,10 @@ switch ( $action ) {
 					) {
 						// Just make it a child of the previous; keep the order.
 						$menu_item_data['menu_item_parent'] = (int) $orders_to_dbids[ $dbids_to_orders[ $menu_item_id ] - 1 ];
+
+						// Reset invalid `menu_item_parent`.
+						$menu_item_data = _wp_reset_invalid_menu_item_parent( $menu_item_data );
+
 						update_post_meta( $menu_item_data['ID'], '_menu_item_menu_item_parent', (int) $menu_item_data['menu_item_parent'] );
 						wp_update_post( $menu_item_data );
 					}
diff --git a/src/wp-includes/nav-menu-template.php b/src/wp-includes/nav-menu-template.php
index 893727c44c..b92cc0c7a8 100644
--- a/src/wp-includes/nav-menu-template.php
+++ b/src/wp-includes/nav-menu-template.php
@@ -199,6 +199,11 @@ function wp_nav_menu( $args = array() ) {
 	$menu_items_tree          = array();
 	$menu_items_with_children = array();
 	foreach ( (array) $menu_items as $menu_item ) {
+		// Fix invalid `menu_item_parent`. See: https://core.trac.wordpress.org/ticket/56926.
+		if ( (int) $menu_item->ID === (int) $menu_item->menu_item_parent ) {
+			$menu_item->menu_item_parent = 0;
+		}
+
 		$sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
 		$menu_items_tree[ $menu_item->ID ]           = $menu_item->menu_item_parent;
 		if ( $menu_item->menu_item_parent ) {
diff --git a/src/wp-includes/nav-menu.php b/src/wp-includes/nav-menu.php
index 87b51182e3..c3750f9e9a 100644
--- a/src/wp-includes/nav-menu.php
+++ b/src/wp-includes/nav-menu.php
@@ -563,6 +563,11 @@ function wp_update_nav_menu_item( $menu_id = 0, $menu_item_db_id = 0, $menu_item
 
 	$menu_item_db_id = (int) $menu_item_db_id;
 
+	// Reset invalid `menu_item_parent`.
+	if ( (int) $args['menu-item-parent-id'] === $menu_item_db_id ) {
+		$args['menu-item-parent-id'] = 0;
+	}
+
 	update_post_meta( $menu_item_db_id, '_menu_item_type', sanitize_key( $args['menu-item-type'] ) );
 	update_post_meta( $menu_item_db_id, '_menu_item_menu_item_parent', (string) ( (int) $args['menu-item-parent-id'] ) );
 	update_post_meta( $menu_item_db_id, '_menu_item_object_id', (string) ( (int) $args['menu-item-object-id'] ) );
@@ -1273,3 +1278,31 @@ function wp_map_nav_menu_locations( $new_nav_menu_locations, $old_nav_menu_locat
 
 	return $new_nav_menu_locations;
 }
+
+/**
+ * Prevents menu items from being their own parent.
+ *
+ * Resets menu_item_parent to 0 when the parent is set to the item itself.
+ * For use before saving `_menu_item_menu_item_parent` in nav-menus.php.
+ *
+ * @since 6.1.2
+ * @access private
+ *
+ * @param array $menu_item_data The menu item data array.
+ * @return array The menu item data with reset menu_item_parent.
+ */
+function _wp_reset_invalid_menu_item_parent( $menu_item_data ) {
+	if ( ! is_array( $menu_item_data ) ) {
+		return $menu_item_data;
+	}
+
+	if (
+		! empty( $menu_item_data['ID'] ) &&
+		! empty( $menu_item_data['menu_item_parent'] ) &&
+		(int) $menu_item_data['ID'] === (int) $menu_item_data['menu_item_parent']
+	) {
+		$menu_item_data['menu_item_parent'] = 0;
+	}
+
+	return $menu_item_data;
+}