Index: src/wp-includes/query.php
===================================================================
--- src/wp-includes/query.php	(revision 27514)
+++ src/wp-includes/query.php	(working copy)
@@ -2268,7 +2268,7 @@
 			// This overrides posts_per_page.
 			if ( ! empty( $q['posts_per_rss'] ) ) {
 				$q['posts_per_page'] = $q['posts_per_rss'];
-			} else { 
+			} else {
 				$q['posts_per_page'] = get_option( 'posts_per_rss' );
 			}
 			$q['nopaging'] = false;
@@ -2671,7 +2671,7 @@
 
 				$orderby_array[] = $orderby;
 			}
-			$orderby = implode( ',', $orderby_array );
+			$orderby = implode( ' ' . $q['order'] . ', ', $orderby_array );
 
 			if ( empty( $orderby ) )
 				$orderby = "$wpdb->posts.post_date ".$q['order'];
Index: tests/phpunit/tests/post/revisions.php
===================================================================
--- tests/phpunit/tests/post/revisions.php	(revision 27514)
+++ tests/phpunit/tests/post/revisions.php	(working copy)
@@ -338,4 +338,20 @@
 			$this->assertTrue( user_can( $author_user_id, 'read_post', $revision->ID ) );
 		}
 	}
+
+	function test_wp_get_posts_revisions_sql() {
+		$post = get_default_post_to_edit( 'post', true );
+
+		add_filter( 'query', array( $this, '_filter_query' ) );
+
+		wp_get_post_revisions( $post->ID );
+
+		remove_filter( 'query', array( $this, '_filter_query' ) );
+	}
+
+	function _filter_query( $sql ) {
+		global $wpdb;
+		$this->assertContains( "ORDER BY $wpdb->posts.post_date DESC, $wpdb->posts.ID DESC", $sql );
+		return $sql;
+	}
 }