diff --git a/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php b/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
index dff85a70e1..581b4ca2a3 100644
--- a/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
+++ b/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
@@ -112,6 +112,28 @@ class WP_Sitemaps_Posts extends WP_Sitemaps_Provider {
 				'loc' => home_url( '/' ),
 			);
 
+			/*
+			 * Get the most recent posts displayed on the homepage,
+			 * and then sort them by their modified date to find
+			 * the date the homepage was approximately last updated.
+			 */
+			$latest_posts = new WP_Query(
+				array(
+					'post_type'              => 'post',
+					'post_status'            => 'publish',
+					'orderby'                => 'date',
+					'order'                  => 'DESC',
+					'no_found_rows'          => true,
+					'update_post_meta_cache' => false,
+					'update_post_term_cache' => false,
+				)
+			);
+
+			if ( ! empty( $latest_posts->posts ) ) {
+				$posts = wp_list_sort( $latest_posts->posts, 'post_modified_gmt', 'DESC' );
+				$sitemap_entry['lastmod'] = wp_date( DATE_W3C, strtotime( $posts[0]->post_modified_gmt ) );
+			}
+
 			/**
 			 * Filters the sitemap entry for the home page when the 'show_on_front' option equals 'posts'.
 			 *
@@ -125,7 +147,8 @@ class WP_Sitemaps_Posts extends WP_Sitemaps_Provider {
 
 		foreach ( $query->posts as $post ) {
 			$sitemap_entry = array(
-				'loc' => get_permalink( $post ),
+				'loc'     => get_permalink( $post ),
+				'lastmod' => wp_date( DATE_W3C, strtotime( $post->post_modified_gmt ) ),
 			);
 
 			/**
diff --git a/tests/phpunit/tests/sitemaps/sitemaps.php b/tests/phpunit/tests/sitemaps/sitemaps.php
index a4fa6b14d7..349bdd961c 100644
--- a/tests/phpunit/tests/sitemaps/sitemaps.php
+++ b/tests/phpunit/tests/sitemaps/sitemaps.php
@@ -251,13 +251,16 @@ class Tests_Sitemaps_Sitemaps extends WP_UnitTestCase {
 
 		$post_list = $providers['posts']->get_url_list( 1, 'page' );
 
+		$post_list_sorted = wp_list_sort( $post_list, 'lastmod', 'DESC' );
+
 		$expected = $this->_get_expected_url_list( 'page', self::$pages );
 
 		// Add the homepage to the front of the URL list.
 		array_unshift(
 			$expected,
 			array(
-				'loc' => home_url( '/' ),
+				'loc'     => home_url( '/' ),
+				'lastmod' => $post_list_sorted[0]['lastmod'],
 			)
 		);
 
@@ -378,7 +381,8 @@ class Tests_Sitemaps_Sitemaps extends WP_UnitTestCase {
 		return array_map(
 			static function ( $post ) {
 				return array(
-					'loc' => get_permalink( $post ),
+					'loc'     => get_permalink( $post ),
+					'lastmod' => get_post_modified_time( DATE_W3C, true, $post ),
 				);
 			},
 			$posts
diff --git a/tests/phpunit/tests/sitemaps/wpSitemapsPosts.php b/tests/phpunit/tests/sitemaps/wpSitemapsPosts.php
index 2bdeb92e8e..70b2fbc250 100644
--- a/tests/phpunit/tests/sitemaps/wpSitemapsPosts.php
+++ b/tests/phpunit/tests/sitemaps/wpSitemapsPosts.php
@@ -59,14 +59,20 @@ class Tests_Sitemaps_wpSitemapsPosts extends WP_UnitTestCase {
 		$url_list      = $posts_provider->get_url_list( 1, 'page' );
 		$sitemap_entry = array_shift( $url_list );
 
-		$this->assertArrayHasKey( 'lastmod', $sitemap_entry );
+		$this->assertEqualSetsWithIndex(
+			array(
+				'loc'     => home_url( '/' ),
+				'lastmod' => '2000-01-01',
+			),
+			$sitemap_entry
+		);
 	}
 
 	/**
 	 * Callback for 'wp_sitemaps_posts_show_on_front_entry' filter.
 	 */
 	public function _show_on_front_entry( $sitemap_entry ) {
-		$sitemap_entry['lastmod'] = wp_date( DATE_W3C, time() );
+		$sitemap_entry['lastmod'] = '2000-01-01';
 
 		return $sitemap_entry;
 	}
@@ -93,7 +99,10 @@ class Tests_Sitemaps_wpSitemapsPosts extends WP_UnitTestCase {
 		$expected = array();
 
 		foreach ( $post_ids as $post_id ) {
-			$expected[] = array( 'loc' => home_url( "?p={$post_id}" ) );
+			$expected[] = array(
+				'loc'     => home_url( "?p={$post_id}" ),
+				'lastmod' => get_post_modified_time( DATE_W3C, true, $post_id ),
+			);
 		}
 
 		// Check that the URL list is still in the order of the post IDs (i.e., sticky post wasn't moved to the front).