diff --git a/wp-includes/post-thumbnail-template.php b/wp-includes/post-thumbnail-template.php
index 7b8d1a2f25..f07302df3a 100644
--- a/wp-includes/post-thumbnail-template.php
+++ b/wp-includes/post-thumbnail-template.php
@@ -13,25 +13,30 @@
  * Check if post has an image attached.
  *
  * @since 2.9.0
+ * @since 4.4.0 `$post` can be a post ID or WP_Post object.
  *
- * @param int $post_id Optional. Post ID.
- * @return bool Whether post has an image attached.
+ * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
+ * @return bool Whether the post has an image attached.
  */
-function has_post_thumbnail( $post_id = null ) {
-	return (bool) get_post_thumbnail_id( $post_id );
+function has_post_thumbnail( $post = null ) {
+	return (bool) get_post_thumbnail_id( $post );
 }
 
 /**
- * Retrieve Post Thumbnail ID.
+ * Retrieve post thumbnail ID.
  *
  * @since 2.9.0
+ * @since 4.4.0 `$post` can be a post ID or WP_Post object.
  *
- * @param int|null $post_id Optional. Post ID.
- * @return mixed
+ * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
+ * @return string|int Post thumbnail ID or empty string.
  */
-function get_post_thumbnail_id( $post_id = null ) {
-	$post_id = ( null === $post_id ) ? get_the_ID() : $post_id;
-	return get_post_meta( $post_id, '_thumbnail_id', true );
+function get_post_thumbnail_id( $post = null ) {
+	$post = get_post( $post );
+	if ( ! $post ) {
+		return '';
+	}
+	return get_post_meta( $post->ID, '_thumbnail_id', true );
 }
 
 /**
@@ -57,7 +62,7 @@ function the_post_thumbnail( $size = 'post-thumbnail', $attr = '' ) {
 }
 
 /**
- * Update cache for thumbnails in the current loop
+ * Update cache for thumbnails in the current loop.
  *
  * @since 3.2.0
  *
@@ -96,16 +101,20 @@ function update_post_thumbnail_cache( $wp_query = null ) {
  * size is used by default, though a different size can be specified instead as needed.
  *
  * @since 2.9.0
+ * @since 4.4.0 `$post` can be a post ID or WP_Post object.
  *
- * @param int $post_id       Post ID. Default is the ID of the `$post` global.
+ * @param int|WP_Post  $post Optional. Post ID or WP_Post object.  Default is global `$post`.
  * @param string|array $size Optional. Registered image size to use, or flat array of height
  *                           and width values. Default 'post-thumbnail'.
  * @param string|array $attr Optional. Query string or array of attributes. Default empty.
- * @return string
+ * @return string The post thumbnail image tag.
  */
-function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $attr = '' ) {
-	$post_id = ( null === $post_id ) ? get_the_ID() : $post_id;
-	$post_thumbnail_id = get_post_thumbnail_id( $post_id );
+function get_the_post_thumbnail( $post = null, $size = 'post-thumbnail', $attr = '' ) {
+	$post = get_post( $post );
+	if ( ! $post ) {
+		return '';
+	}
+	$post_thumbnail_id = get_post_thumbnail_id( $post );
 
 	/**
 	 * Filter the post thumbnail size.
@@ -125,11 +134,11 @@ function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $att
 		 *
 		 * @since 2.9.0
 		 *
-		 * @param string $post_id           The post ID.
+		 * @param int    $post_id           The post ID.
 		 * @param string $post_thumbnail_id The post thumbnail ID.
 		 * @param string $size              The post thumbnail size.
 		 */
-		do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
+		do_action( 'begin_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );
 		if ( in_the_loop() )
 			update_post_thumbnail_cache();
 		$html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );
@@ -139,11 +148,11 @@ function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $att
 		 *
 		 * @since 2.9.0
 		 *
-		 * @param string $post_id           The post ID.
+		 * @param int    $post_id           The post ID.
 		 * @param string $post_thumbnail_id The post thumbnail ID.
 		 * @param string $size              The post thumbnail size.
 		 */
-		do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
+		do_action( 'end_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );
 
 	} else {
 		$html = '';
@@ -154,10 +163,10 @@ function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $att
 	 * @since 2.9.0
 	 *
 	 * @param string $html              The post thumbnail HTML.
-	 * @param string $post_id           The post ID.
+	 * @param int    $post_id           The post ID.
 	 * @param string $post_thumbnail_id The post thumbnail ID.
 	 * @param string $size              The post thumbnail size.
 	 * @param string $attr              Query string of attributes.
 	 */
-	return apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr );
+	return apply_filters( 'post_thumbnail_html', $html, $post->ID, $post_thumbnail_id, $size, $attr );
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 4012a01fb7..61e66b4f2c 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34166';
+$wp_version = '4.4-alpha-34167';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.