diff --git a/src/wp-includes/comment.php b/src/wp-includes/comment.php
index f3746750a2..20b208ed9e 100644
--- a/src/wp-includes/comment.php
+++ b/src/wp-includes/comment.php
@@ -221,6 +221,15 @@ function get_comments( $args = '' ) {
  * @since 3.1.0
  */
 class WP_Comment_Query {
+	/**
+	 * SQL for database query.
+	 *
+	 * @since 4.0.1
+	 * @access public
+	 * @var string
+	 */
+	public $request;
+
 	/**
 	 * Metadata query container
 	 *
@@ -578,18 +587,19 @@ class WP_Comment_Query {
 		if ( $groupby ) {
 			$groupby = 'GROUP BY ' . $groupby;
 		}
-		$query = "SELECT $fields FROM $wpdb->comments $join WHERE $where $groupby ORDER BY $orderby $order $limits";
+
+		$this->request = "SELECT $fields FROM $wpdb->comments $join WHERE $where $groupby $orderby $order $limits";
 
 		if ( $this->query_vars['count'] ) {
-			return $wpdb->get_var( $query );
+			return $wpdb->get_var( $this->request );
 		}
 
 		if ( 'ids' == $this->query_vars['fields'] ) {
-			$this->comments = $wpdb->get_col( $query );
+			$this->comments = $wpdb->get_col( $this->request );
 			return array_map( 'intval', $this->comments );
 		}
 
-		$results = $wpdb->get_results( $query );
+		$results = $wpdb->get_results( $this->request );
 		/**
 		 * Filter the comment query results.
 		 *
diff --git a/tests/phpunit/tests/comment/query.php b/tests/phpunit/tests/comment/query.php
index 61f39acd22..0d8bb02c54 100644
--- a/tests/phpunit/tests/comment/query.php
+++ b/tests/phpunit/tests/comment/query.php
@@ -516,4 +516,65 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 
 		$this->assertEquals( array( $c1, $c2, $c3, $c4, $c5 ), $found );
 	}
+
+	public function test_orderby_default() {
+		$q = new WP_Comment_Query();
+		$q->query( array() );
+
+		$this->assertContains( 'ORDER BY comment_date_gmt', $q->request );
+	}
+
+	public function test_orderby_single() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => 'comment_agent',
+		) );
+
+		$this->assertContains( 'ORDER BY comment_agent', $q->request );
+	}
+
+	public function test_orderby_single_invalid() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => 'foo',
+		) );
+
+		$this->assertContains( 'ORDER BY comment_date_gmt', $q->request );
+	}
+
+	public function test_orderby_comma_separated() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => 'comment_agent, comment_approved',
+		) );
+
+		$this->assertContains( 'ORDER BY comment_agent, comment_approved', $q->request );
+	}
+
+	public function test_orderby_array() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => array( 'comment_agent', 'comment_approved' ),
+		) );
+
+		$this->assertContains( 'ORDER BY comment_agent, comment_approved', $q->request );
+	}
+
+	public function test_orderby_array_contains_invalid_item() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => array( 'comment_agent', 'foo', 'comment_approved' ),
+		) );
+
+		$this->assertContains( 'ORDER BY comment_agent, comment_approved', $q->request );
+	}
+
+	public function test_orderby_array_contains_all_invalid_items() {
+		$q = new WP_Comment_Query();
+		$q->query( array(
+			'orderby' => array( 'foo', 'bar', 'baz' ),
+		) );
+
+		$this->assertContains( 'ORDER BY comment_date_gmt', $q->request );
+	}
 }