diff --git a/src/wp-includes/comment.php b/src/wp-includes/comment.php
index 57eaaada3f..c84ecc2320 100644
--- a/src/wp-includes/comment.php
+++ b/src/wp-includes/comment.php
@@ -257,7 +257,8 @@ class WP_Comment_Query {
 	 * Execute the query
 	 *
 	 * @since 3.1.0
-	 * @since 4.1.0 Introduced 'comment__in', 'comment__not_in',
+	 * @since 4.1.0 Introduced 'comment__in', 'comment__not_in', 'post_author__in',
+	 *              'post_author__not_in', 'author__in', 'author__not_in',
 	 *              'post__in', and 'post__not_in' to $query_vars.
 	 *
 	 * @param string|array $query_vars
@@ -268,6 +269,8 @@ class WP_Comment_Query {
 
 		$defaults = array(
 			'author_email' => '',
+			'author__in' => '',
+			'author__not_in' => '',
 			'fields' => '',
 			'ID' => '',
 			'comment__in' => '',
@@ -278,6 +281,8 @@ class WP_Comment_Query {
 			'orderby' => '',
 			'order' => 'DESC',
 			'parent' => '',
+			'post_author__in' => '',
+			'post_author__not_in' => '',
 			'post_ID' => '',
 			'post_id' => 0,
 			'post__in' => '',
@@ -467,13 +472,42 @@ class WP_Comment_Query {
 			);
 		}
 
+		// If any post-related query vars are passed, join the posts table.
+		$join_posts_table = false;
 		$plucked = wp_array_slice_assoc( $this->query_vars, array( 'post_author', 'post_name', 'post_parent', 'post_status', 'post_type' ) );
 		$post_fields = array_filter( $plucked );
 
 		if ( ! empty( $post_fields ) ) {
-			$join = "JOIN $wpdb->posts ON $wpdb->posts.ID = $wpdb->comments.comment_post_ID";
-			foreach( $post_fields as $field_name => $field_value )
+			$join_posts_table = true;
+			foreach ( $post_fields as $field_name => $field_value ) {
 				$where .= $wpdb->prepare( " AND {$wpdb->posts}.{$field_name} = %s", $field_value );
+			}
+		}
+
+		// Comment author IDs for an IN clause.
+		if ( ! empty( $this->query_vars['author__in'] ) ) {
+			$where .= ' AND user_id IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['author__in'] ) ) . ' )';
+		}
+
+		// Comment author IDs for a NOT IN clause.
+		if ( ! empty( $this->query_vars['author__not_in'] ) ) {
+			$where .= ' AND user_id NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['author__not_in'] ) ) . ' )';
+		}
+
+		// Post author IDs for an IN clause.
+		if ( ! empty( $this->query_vars['post_author__in'] ) ) {
+			$join_posts_table = true;
+			$where .= ' AND post_author IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post_author__in'] ) ) . ' )';
+		}
+
+		// Post author IDs for a NOT IN clause.
+		if ( ! empty( $this->query_vars['post_author__not_in'] ) ) {
+			$join_posts_table = true;
+			$where .= ' AND post_author NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post_author__not_in'] ) ) . ' )';
+		}
+
+		if ( $join_posts_table ) {
+			$join = "JOIN $wpdb->posts ON $wpdb->posts.ID = $wpdb->comments.comment_post_ID";
 		}
 
 		if ( ! empty( $this->meta_query->queries ) ) {
diff --git a/tests/phpunit/tests/comment/query.php b/tests/phpunit/tests/comment/query.php
index 17969a4fdc..9e7ba92da4 100644
--- a/tests/phpunit/tests/comment/query.php
+++ b/tests/phpunit/tests/comment/query.php
@@ -270,4 +270,94 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 
 		$this->assertEqualSets( array( $c3 ), $comment_ids );
 	}
+
+	/**
+	 * @ticket 29885
+	 */
+	function test_fields_post_author__in() {
+		$author_id1 = 105;
+		$author_id2 = 106;
+
+		$p1 = $this->factory->post->create( array( 'post_author' => $author_id1	) );
+		$p2 = $this->factory->post->create( array( 'post_author' => $author_id1	) );
+		$p3 = $this->factory->post->create( array( 'post_author' => $author_id2	) );
+
+		$c1 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c2 = $this->factory->comment->create( array( 'comment_post_ID' => $p2, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c3 = $this->factory->comment->create( array( 'comment_post_ID' => $p3, 'user_id' => 1, 'comment_approved' => '1' ) );
+
+		$comment_ids = get_comments( array(
+			'fields' => 'ids',
+			'post_author__in' => array( $author_id1 ),
+		) );
+
+		$this->assertEqualSets( array( $c1, $c2 ), $comment_ids );
+	}
+
+	/**
+	 * @ticket 29885
+	 */
+	function test_fields_post_author__not_in() {
+		$author_id1 = 111;
+		$author_id2 = 112;
+
+		$p1 = $this->factory->post->create( array( 'post_author' => $author_id1	) );
+		$p2 = $this->factory->post->create( array( 'post_author' => $author_id1	) );
+		$p3 = $this->factory->post->create( array( 'post_author' => $author_id2	) );
+
+		$c1 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c2 = $this->factory->comment->create( array( 'comment_post_ID' => $p2, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c3 = $this->factory->comment->create( array( 'comment_post_ID' => $p3, 'user_id' => 1, 'comment_approved' => '1' ) );
+
+		$comment_ids = get_comments( array(
+			'fields' => 'ids',
+			'post_author__not_in' => array( $author_id1 ),
+		) );
+
+		$this->assertEqualSets( array( $c3 ), $comment_ids );
+	}
+
+        /**
+         * @ticket 29885
+         */
+	function test_fields_author__in() {
+		$p1 = $this->factory->post->create();
+		$p2 = $this->factory->post->create();
+		$p3 = $this->factory->post->create();
+		$p4 = $this->factory->post->create();
+
+		$c1 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c2 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 2, 'comment_approved' => '1' ) );
+		$c3 = $this->factory->comment->create( array( 'comment_post_ID' => $p2, 'user_id' => 3, 'comment_approved' => '1' ) );
+		$c4 = $this->factory->comment->create( array( 'comment_post_ID' => $p4, 'user_id' => 4, 'comment_approved' => '1' ) );
+
+		$comment_ids = get_comments( array(
+			'fields' => 'ids',
+			'author__in' => array( 1, 3 ),
+		) );
+
+		$this->assertEqualSets( array( $c1, $c3 ), $comment_ids );
+	}
+
+        /**
+         * @ticket 29885
+         */
+	function test_fields_author__not_in() {
+		$p1 = $this->factory->post->create();
+		$p2 = $this->factory->post->create();
+		$p3 = $this->factory->post->create();
+		$p4 = $this->factory->post->create();
+
+		$c1 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 1, 'comment_approved' => '1' ) );
+		$c2 = $this->factory->comment->create( array( 'comment_post_ID' => $p1, 'user_id' => 2, 'comment_approved' => '1' ) );
+		$c3 = $this->factory->comment->create( array( 'comment_post_ID' => $p2, 'user_id' => 3, 'comment_approved' => '1' ) );
+		$c4 = $this->factory->comment->create( array( 'comment_post_ID' => $p4, 'user_id' => 4, 'comment_approved' => '1' ) );
+
+		$comment_ids = get_comments( array(
+			'fields' => 'ids',
+			'author__not_in' => array( 1, 2 ),
+		) );
+
+		$this->assertEqualSets( array( $c3, $c4 ), $comment_ids );
+	}
 }