diff --git wp-includes/feed.php wp-includes/feed.php
index ecb4a25293..154ecc08b7 100644
--- wp-includes/feed.php
+++ wp-includes/feed.php
@@ -662,6 +662,8 @@ function get_feed_build_date( $format ) {
 	// Extract the post modified times from the posts.
 	$modified_times = wp_list_pluck( $wp_query->posts, 'post_modified_gmt' );
 
+	$modified_times = array_merge( $modified_times, wp_list_pluck( $wp_query->posts, 'post_date_gmt' ) );
+
 	// If this is a comment feed, check those objects too.
 	if ( $wp_query->is_comment_feed() && $wp_query->comment_count ) {
 		// Extract the comment modified times from the comments.