diff --git src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
index 30ddafc..1d9abfe 100644
--- src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
@@ -170,7 +170,7 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 		do_action( 'rest_insert_attachment', $attachment, $request, true );
 
 		// Include admin functions to get access to wp_generate_attachment_metadata().
-		require_once ABSPATH . 'wp-admin/includes/admin.php';
+		require_once ABSPATH . 'wp-admin/includes/image.php';
 
 		wp_update_attachment_metadata( $id, wp_generate_attachment_metadata( $id, $file ) );
 
@@ -513,8 +513,8 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 		// Get the content-type.
 		$type = array_shift( $headers['content_type'] );
 
-		/** Include admin functions to get access to wp_tempnam() and wp_handle_sideload() */
-		require_once ABSPATH . 'wp-admin/includes/admin.php';
+		/** Include to get access to wp_tempnam() and wp_handle_sideload() */
+		require_once ABSPATH . 'wp-admin/includes/file.php';
 
 		// Save the file.
 		$tmpfname = wp_tempnam( $filename );
@@ -703,8 +703,8 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 			$overrides['action'] = 'wp_handle_mock_upload';
 		}
 
-		/** Include admin functions to get access to wp_handle_upload() */
-		require_once ABSPATH . 'wp-admin/includes/admin.php';
+		/** Include to get access to wp_handle_upload() */
+		require_once ABSPATH . 'wp-admin/includes/file.php';
 
 		$file = wp_handle_upload( $files['file'], $overrides );