diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php
index 0a2cf5d49b..f99a201974 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php
@@ -220,7 +220,15 @@ class WP_REST_Autosaves_Controller extends WP_REST_Revisions_Controller {
 		$prepared_post->ID = $post->ID;
 		$user_id           = get_current_user_id();
 
-		if ( ( 'draft' === $post->post_status || 'auto-draft' === $post->post_status ) && $post->post_author == $user_id ) {
+		// We need to check post lock to ensure the original author didn't leave their browser tab open.
+		if ( ! function_exists( 'wp_check_post_lock' ) ) {
+			require_once ABSPATH . 'wp-admin/includes/post.php';
+		}
+
+		$post_lock = wp_check_post_lock( $post->ID );
+		$is_draft  = 'draft' === $post->post_status || 'auto-draft' === $post->post_status;
+
+		if ( $is_draft && (int) $post->post_author === $user_id && ! $post_lock ) {
 			// Draft posts for the same author: autosaving updates the post and does not create a revision.
 			// Convert the post object to an array and add slashes, wp_update_post() expects escaped array.
 			$autosave_id = wp_update_post( wp_slash( (array) $prepared_post ), true );
diff --git a/tests/phpunit/tests/rest-api/rest-autosaves-controller.php b/tests/phpunit/tests/rest-api/rest-autosaves-controller.php
index 0128c0dcec..2a7eacb8b9 100644
--- a/tests/phpunit/tests/rest-api/rest-autosaves-controller.php
+++ b/tests/phpunit/tests/rest-api/rest-autosaves-controller.php
@@ -607,4 +607,71 @@ class WP_Test_REST_Autosaves_Controller extends WP_Test_REST_Post_Type_Controlle
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertNotEquals( 'garbage', get_post( self::$draft_page_id )->comment_status );
 	}
+
+	/**
+	 * Test ensuring that autosave from the original author doesn't overwrite changes after it has been taken over by a 2nd author.
+	 *
+	 * @ticket 55659
+	 */
+	public function test_rest_autosave_draft_post_locked_to_different_author() {
+
+		// Create a post by the editor.
+		$post_data = array(
+			'post_content' => 'Test post content',
+			'post_title'   => 'Test post title',
+			'post_excerpt' => 'Test post excerpt',
+			'post_author'  => self::$editor_id,
+			'post_status'  => 'draft',
+		);
+		$post_id   = wp_insert_post( $post_data );
+
+		// Set the post lock to the contributor, simulating a takeover of the post.
+		wp_set_current_user( self::$contributor_id );
+		wp_set_post_lock( $post_id );
+
+		// Update the post with new data from the contributor.
+		$updated_post_data = array(
+			'ID'           => $post_id,
+			'post_content' => 'New post content from the contributor',
+			'post_title'   => 'New post title',
+		);
+		wp_update_post( $updated_post_data );
+
+		// Set the current user to the editor and initiate an autosave with some new data.
+		wp_set_current_user( self::$editor_id );
+		$autosave_data = array(
+			'id'      => $post_id,
+			'content' => 'Updated post content',
+			'excerpt' => 'A new excerpt to test',
+			'title'   => $post_data['post_title'],
+		);
+
+		// Initiate an autosave via the REST API as Gutenberg does.
+		$request = new WP_REST_Request( 'POST', '/wp/v2/posts/' . self::$post_id . '/autosaves' );
+		$request->add_header( 'content-type', 'application/json' );
+		$request->set_body( wp_json_encode( $autosave_data ) );
+
+		$response = rest_get_server()->dispatch( $request );
+		$new_data = $response->get_data();
+
+		// The current version of our test post.
+		$current_post = get_post( $post_id );
+
+		// The new data from the autosave should have its parent ID set to the original post ID.
+		$this->assertSame( $post_id, $new_data['parent'] );
+
+		// The post title and content should still be the updated versions from the contributor.
+		$this->assertSame( $current_post->post_title, $updated_post_data['post_title'] );
+		$this->assertSame( $current_post->post_content, $updated_post_data['post_content'] );
+
+		// The excerpt should have stayed the same.
+		$this->assertSame( $current_post->post_excerpt, $post_data['post_excerpt'] );
+
+		$autosave_post = wp_get_post_autosave( $post_id );
+
+		// Has changes.
+		$this->assertSame( $autosave_data['content'], $autosave_post->post_content );
+
+		wp_delete_post( $post_id );
+	}
 }