diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index 50b0aa3b76..9c6fac8755 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -6620,16 +6620,20 @@ function get_posts_by_author_sql( $post_type, $full = true, $post_author = null,
  * @return string The date of the last post, or false on failure.
  */
 function get_lastpostdate( $timezone = 'server', $post_type = 'any' ) {
+	$date = _get_last_post_time( $timezone, 'date', $post_type );
+
 	/**
 	 * Filters the most recent time that a post on the site was published.
 	 *
 	 * @since 2.3.0
+	 * @since 5.5.0 Added the `$post_type` parameter.
 	 *
-	 * @param string|false $date     Date the last post was published. False on failure.
-	 * @param string       $timezone Location to use for getting the post published date.
-	 *                               See get_lastpostdate() for accepted `$timezone` values.
+	 * @param string|false $date      Date the last post was published. False on failure.
+	 * @param string       $timezone  Location to use for getting the post published date.
+	 *                                See get_lastpostdate() for accepted `$timezone` values.
+	 * @param string       $post_type The post type to check.
 	 */
-	return apply_filters( 'get_lastpostdate', _get_last_post_time( $timezone, 'date', $post_type ), $timezone );
+	return apply_filters( 'get_lastpostdate', $date, $timezone, $post_type );
 }
 
 /**
@@ -6661,13 +6665,14 @@ function get_lastpostmodified( $timezone = 'server', $post_type = 'any' ) {
 	 * @param string       $post_type        The post type to check.
 	 */
 	$lastpostmodified = apply_filters( 'pre_get_lastpostmodified', false, $timezone, $post_type );
+
 	if ( false !== $lastpostmodified ) {
 		return $lastpostmodified;
 	}
 
 	$lastpostmodified = _get_last_post_time( $timezone, 'modified', $post_type );
+	$lastpostdate     = get_lastpostdate( $timezone, $post_type );
 
-	$lastpostdate = get_lastpostdate( $timezone );
 	if ( $lastpostdate > $lastpostmodified ) {
 		$lastpostmodified = $lastpostdate;
 	}
@@ -6676,13 +6681,15 @@ function get_lastpostmodified( $timezone = 'server', $post_type = 'any' ) {
 	 * Filters the most recent time that a post was modified.
 	 *
 	 * @since 2.3.0
+	 * @since 5.5.0 Added the `$post_type` parameter.
 	 *
 	 * @param string|false $lastpostmodified The most recent time that a post was modified, in 'Y-m-d H:i:s' format.
 	 *                                       False on failure.
 	 * @param string       $timezone         Location to use for getting the post modified date.
 	 *                                       See get_lastpostdate() for accepted `$timezone` values.
+	 * @param string       $post_type        The post type to check.
 	 */
-	return apply_filters( 'get_lastpostmodified', $lastpostmodified, $timezone );
+	return apply_filters( 'get_lastpostmodified', $lastpostmodified, $timezone, $post_type );
 }
 
 /**
diff --git a/tests/phpunit/tests/post/getLastPostDate.php b/tests/phpunit/tests/post/getLastPostDate.php
new file mode 100644
index 0000000000..022228638d
--- /dev/null
+++ b/tests/phpunit/tests/post/getLastPostDate.php
@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * @group post
+ */
+class Tests_Post_GetLastPostDate extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 47777
+	 */
+	public function test_get_lastpostdate() {
+		$post_post_date = '2020-01-30 16:09:28';
+		$book_post_date = '2019-02-28 18:11:30';
+
+		// Register book post type.
+		register_post_type( 'book', array( 'has_archive' => true ) );
+
+		// Create a simple post.
+		$simple_post_id = self::factory()->post->create(
+			array(
+				'post_title' => 'Simple Post',
+				'post_type'  => 'post',
+				'post_date'  => $post_post_date,
+			)
+		);
+
+		// Create custom type post.
+		$book_cpt_id = self::factory()->post->create(
+			array(
+				'post_title' => 'Book CPT',
+				'post_type'  => 'book',
+				'post_date'  => $book_post_date,
+			)
+		);
+
+		$this->assertEquals( $post_post_date, get_lastpostdate( 'blog', 'post' ) );
+		$this->assertEquals( $book_post_date, get_lastpostdate( 'blog', 'book' ) );
+	}
+}
diff --git a/tests/phpunit/tests/post/getLastPostModified.php b/tests/phpunit/tests/post/getLastPostModified.php
new file mode 100644
index 0000000000..1c83ff042a
--- /dev/null
+++ b/tests/phpunit/tests/post/getLastPostModified.php
@@ -0,0 +1,67 @@
+<?php
+
+/**
+ * @group post
+ */
+class Tests_Post_GetLastPostModified extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 47777
+	 */
+	public function test_get_lastpostmodified() {
+		global $wpdb;
+
+		$post_post_date     = '2020-01-30 16:09:28';
+		$post_post_modified = '2020-02-28 17:10:29';
+
+		$book_post_date     = '2019-03-30 20:09:28';
+		$book_post_modified = '2019-04-30 21:10:29';
+
+		// Register book post type.
+		register_post_type( 'book', array( 'has_archive' => true ) );
+
+		// Create a simple post.
+		$simple_post_id = self::factory()->post->create(
+			array(
+				'post_title' => 'Simple Post',
+				'post_type'  => 'post',
+				'post_date'  => $post_post_date,
+			)
+		);
+
+		// Create custom type post.
+		$book_cpt_id = self::factory()->post->create(
+			array(
+				'post_title' => 'Book CPT',
+				'post_type'  => 'book',
+				'post_date'  => $book_post_date,
+			)
+		);
+
+		// Update `post_modified` and `post_modified_gmt`.
+		$wpdb->update(
+			$wpdb->posts,
+			array(
+				'post_modified'     => $post_post_modified,
+				'post_modified_gmt' => $post_post_modified,
+			),
+			array(
+				'ID' => $simple_post_id,
+			)
+		);
+
+		$wpdb->update(
+			$wpdb->posts,
+			array(
+				'post_modified'     => $book_post_modified,
+				'post_modified_gmt' => $book_post_modified,
+			),
+			array(
+				'ID' => $book_cpt_id,
+			)
+		);
+
+		$this->assertEquals( $post_post_modified, get_lastpostmodified( 'blog', 'post' ) );
+		$this->assertEquals( $book_post_modified, get_lastpostmodified( 'blog', 'book' ) );
+	}
+}