diff --git a/src/wp-includes/class-wp.php b/src/wp-includes/class-wp.php
index 2fe76fc8b7..78259defb5 100644
--- a/src/wp-includes/class-wp.php
+++ b/src/wp-includes/class-wp.php
@@ -568,8 +568,15 @@ class WP {
 		// We will 404 for paged queries, as no posts were found.
 		if ( ! is_paged() ) {
 
+			// Don't 404 for authors without posts as long as they matched an author on this site.
+			$author = get_query_var( 'author' );
+			if ( is_author() && is_numeric( $author ) && $author > 0 && is_user_member_of_blog( $author ) ) {
+				status_header( 200 );
+				return;
+			}
+
 			// Don't 404 for these queries if they matched an object.
-			if ( ( is_tag() || is_category() || is_tax() || is_author() || is_post_type_archive() ) && $wp_query->get_queried_object() ) {
+			if ( ( is_tag() || is_category() || is_tax() || is_post_type_archive() ) && get_queried_object() ) {
 				status_header( 200 );
 				return;
 			}
diff --git a/tests/phpunit/tests/ms.php b/tests/phpunit/tests/ms.php
index bcd597965b..f307ff735d 100644
--- a/tests/phpunit/tests/ms.php
+++ b/tests/phpunit/tests/ms.php
@@ -1219,6 +1219,48 @@ class Tests_MS extends WP_UnitTestCase {
 		$this->assertEquals( $ids['wordpress.net/'],
 			get_network_by_path( 'site1.wordpress.net', '/three/' )->id );
 	}
+
+	/**
+	 * @ticket 20601
+	 */
+	function test_user_member_of_blog() {
+		global $wp_rewrite;
+
+		$this->factory->blog->create();
+		$user_id = $this->factory->user->create();
+		$this->factory->blog->create( array( 'user_id' => $user_id ) );
+
+		$blogs = get_blogs_of_user( $user_id );
+		$this->assertCount( 2, $blogs );
+		$first = reset( $blogs )->userblog_id;
+		remove_user_from_blog( $user_id, $first );
+
+		$blogs = get_blogs_of_user( $user_id );
+		$second = reset( $blogs )->userblog_id;
+		$this->assertCount( 1, $blogs );
+
+		switch_to_blog( $first );
+		$wp_rewrite->init();
+
+		$this->go_to( get_author_posts_url( $user_id ) );
+		$this->assertQueryTrue( 'is_404' );
+
+		switch_to_blog( $second );
+		$wp_rewrite->init();
+
+		$this->go_to( get_author_posts_url( $user_id ) );
+		$this->assertQueryTrue( 'is_author', 'is_archive' );
+
+		add_user_to_blog( $first, $user_id, 'administrator' );
+		$blogs = get_blogs_of_user( $user_id );
+		$this->assertCount( 2, $blogs );
+
+		switch_to_blog( $first );
+		$wp_rewrite->init();
+
+		$this->go_to( get_author_posts_url( $user_id ) );
+		$this->assertQueryTrue( 'is_author', 'is_archive' );
+	}
 }
 
 endif;