diff --git a/inc/namespace.php b/inc/namespace.php
index 8fd2f16..79b3522 100644
--- a/inc/namespace.php
+++ b/inc/namespace.php
@@ -428,6 +428,8 @@ function validate_authors( $authors, WP_REST_Request $request, string $param, st
 
 	/** @var WP_User[] */
 	$users = get_users( [
+		// Check all sites.
+		'blog_id' => 0,
 		'include' => $authors,
 		'orderby' => 'include',
 	] );
diff --git a/inc/template.php b/inc/template.php
index a573de3..761288a 100644
--- a/inc/template.php
+++ b/inc/template.php
@@ -53,6 +53,8 @@ function get_authors( WP_Post $post ) : array {
 
 	/** @var WP_User[] */
 	$users = get_users( [
+		// Check all sites.
+		'blog_id' => 0,
 		'include' => $author_ids,
 		'orderby' => 'include',
 	] );
@@ -155,6 +157,8 @@ function set_authors( WP_Post $post, array $authors ) : array {
 
 	/** @var WP_User[] */
 	$users = get_users( [
+		// Check all sites.
+		'blog_id' => 0,
 		'include' => $authors,
 		'orderby' => 'include',
 	] );
diff --git a/tests/phpunit/test-multisite.php b/tests/phpunit/test-multisite.php
new file mode 100644
index 0000000..6ab46e2
--- /dev/null
+++ b/tests/phpunit/test-multisite.php
@@ -0,0 +1,95 @@
+<?php
+/**
+ * Multisite tests for the plugin.
+ *
+ * @package authorship
+ */
+
+declare( strict_types=1 );
+
+namespace Authorship\Tests;
+
+use const Authorship\POSTS_PARAM;
+
+/**
+ * @group ms-required
+ */
+class TestMultisite extends TestCase {
+	/**
+	 * Super admin.
+	 *
+	 * @var \WP_User
+	 */
+	protected static $super_admin;
+
+	/**
+	 * Sub site.
+	 *
+	 * @var \WP_Site
+	 */
+	protected static $sub_site;
+
+	/**
+	 * Set up class test fixtures.
+	 *
+	 * @param \WP_UnitTest_Factory $factory Test factory.
+	 */
+	public static function wpSetUpBeforeClass( \WP_UnitTest_Factory $factory ) {
+		parent::wpSetUpBeforeClass( $factory );
+
+		// Create a super admin user.
+		self::$super_admin = $factory->user->create_and_get( [
+			'role' => 'administrator',
+			'display_name' => 'Super Admin',
+			'user_email' => 'super-admin.role@example.org',
+		] );
+
+		grant_super_admin( self::$super_admin->ID );
+
+		// Create a subsite.
+		self::$sub_site = $factory->blog->create_and_get( [
+			'domain' => 'example.org',
+			'path' => '/subsite',
+			'title' => 'Authorship Sub Site',
+			'user_id' => self::$users['admin']->ID,
+		] );
+	}
+
+	public function testSuperAdminWithNoRoleOnSite() {
+		// Change site.
+		switch_to_blog( self::$sub_site->blog_id );
+
+		// Confirm no role on current site.
+		$super_admin = get_user_by( 'ID', self::$super_admin->ID );
+		$this->assertEmpty( $super_admin->roles );
+
+		$factory = self::factory()->post;
+
+		// Attributed to Super Admin, owned by Admin.
+		$post = $factory->create_and_get( [
+			'post_author' => self::$users['admin']->ID,
+			POSTS_PARAM   => [
+				self::$super_admin->ID,
+			],
+		] );
+
+		// Check super admin ID is stored.
+		$author_ids = \Authorship\get_author_ids( $post );
+		$this->assertSame( [ self::$super_admin->ID ], $author_ids );
+
+		$author_url = get_author_posts_url( self::$super_admin->ID );
+		$this->assertTrue( strpos( $author_url, '/subsite/' ) !== false );
+		$this->go_to( $author_url );
+
+		/** @var \WP_Query */
+		global $wp_query, $authordata;
+
+		$this->assertQueryTrue( 'is_author', 'is_archive' );
+		$this->assertTrue( is_author( self::$super_admin->ID ) );
+		$this->assertSame( [ $post->ID ], wp_list_pluck( $wp_query->posts, 'ID' ) );
+		$this->assertSame( self::$super_admin->ID, $authordata->ID );
+
+		restore_current_blog();
+	}
+
+}