diff --git a/src/wp-includes/comment-template.php b/src/wp-includes/comment-template.php
index f4c904bc88..64b4ba8e53 100644
--- a/src/wp-includes/comment-template.php
+++ b/src/wp-includes/comment-template.php
@@ -1286,11 +1286,16 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 		'order' => 'ASC',
 		'status'  => 'approve',
 		'post_id' => $post->ID,
-		'hierarchical' => 'threaded',
 		'no_found_rows' => false,
 		'update_comment_meta_cache' => false, // We lazy-load comment meta for performance.
 	);
 
+	if ( get_option('thread_comments') ) {
+		$comment_args['hierarchical'] = 'threaded';
+	} else {
+		$comment_args['hierarchical'] = false;
+	}
+
 	if ( $user_ID ) {
 		$comment_args['include_unapproved'] = array( $user_ID );
 	} elseif ( ! empty( $comment_author_email ) ) {
@@ -1336,18 +1341,22 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 	$_comments = $comment_query->comments;
 
 	// Trees must be flattened before they're passed to the walker.
-	$comments_flat = array();
-	foreach ( $_comments as $_comment ) {
-		$comments_flat[]  = $_comment;
-		$comment_children = $_comment->get_children( array(
-			'format' => 'flat',
-			'status' => $comment_args['status'],
-			'orderby' => $comment_args['orderby']
-		) );
+	if ( $comment_args['hierarchical'] ) {
+		$comments_flat = array();
+		foreach ( $_comments as $_comment ) {
+			$comments_flat[]  = $_comment;
+			$comment_children = $_comment->get_children( array(
+				'format' => 'flat',
+				'status' => $comment_args['status'],
+				'orderby' => $comment_args['orderby']
+			) );
 
-		foreach ( $comment_children as $comment_child ) {
-			$comments_flat[] = $comment_child;
+			foreach ( $comment_children as $comment_child ) {
+				$comments_flat[] = $comment_child;
+			}
 		}
+	} else {
+		$comments_flat = $_comments;
 	}
 
 	/**
diff --git a/tests/phpunit/tests/comment/commentsTemplate.php b/tests/phpunit/tests/comment/commentsTemplate.php
index 308df77c24..3c4ddd368b 100644
--- a/tests/phpunit/tests/comment/commentsTemplate.php
+++ b/tests/phpunit/tests/comment/commentsTemplate.php
@@ -689,4 +689,43 @@ class Tests_Comment_CommentsTemplate extends WP_UnitTestCase {
 		$commenter['comment_author_email'] = 'foo@example.com';
 		return $commenter;
 	}
+
+	/**
+	 * @ticket 35378
+	 */
+	public function test_hierarchy_should_be_ignored_when_threading_is_disabled() {
+		$now = time();
+		$p = self::factory()->post->create();
+		$comment_1 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_content' => '1',
+			'comment_approved' => '1',
+			'comment_date_gmt' => date( 'Y-m-d H:i:s', $now - 100 ),
+		) );
+		$comment_2 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_content' => '2',
+			'comment_approved' => '1',
+			'comment_date_gmt' => date( 'Y-m-d H:i:s', $now - 300 ),
+		) );
+		$comment_3 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_content' => '3',
+			'comment_approved' => '1',
+			'comment_parent' => $comment_1,
+			'comment_date_gmt' => date( 'Y-m-d H:i:s', $now - 200 ),
+		) );
+
+		update_option( 'comment_order', 'asc' );
+		update_option( 'thread_comments', 0 );
+
+		$this->go_to( get_permalink( $p ) );
+		$found = get_echo( 'comments_template' );
+
+		// Find the found comments in the markup.
+		preg_match_all( '|id="comment-([0-9]+)|', $found, $matches );
+
+		$found_cids = array_map( 'intval', $matches[1] );
+		$this->assertSame( array( $comment_2, $comment_3, $comment_1 ), $found_cids );
+	}
 }