diff --git a/src/wp-includes/post-thumbnail-template.php b/src/wp-includes/post-thumbnail-template.php
index 91201e7994..64c8494ca6 100644
--- a/src/wp-includes/post-thumbnail-template.php
+++ b/src/wp-includes/post-thumbnail-template.php
@@ -57,7 +57,7 @@ function update_post_thumbnail_cache( $wp_query = null ) {
 	if ( ! $wp_query )
 		$wp_query = $GLOBALS['wp_query'];
 
-	if ( $wp_query->thumbnails_cached )
+	if ( $wp_query->thumbnails_cached || ! $wp_query->posts )
 		return;
 
 	$thumb_ids = array();
@@ -69,7 +69,7 @@ function update_post_thumbnail_cache( $wp_query = null ) {
 	if ( ! empty ( $thumb_ids ) ) {
 		_prime_post_caches( $thumb_ids, false, true );
 	}
-
+	
 	$wp_query->thumbnails_cached = true;
 }
 
diff --git a/tests/phpunit/tests/post/thumbnails.php b/tests/phpunit/tests/post/thumbnails.php
new file mode 100644
index 0000000000..2584bbad2d
--- /dev/null
+++ b/tests/phpunit/tests/post/thumbnails.php
@@ -0,0 +1,30 @@
+<?php
+/**
+ * @group post
+ * @group thumbnails
+ */
+class Tests_Post_Thumbnails extends WP_UnitTestCase {
+	/**
+	 * @ticket 26321
+	 */
+	function test_update_post_thumbnail_cache() {
+		update_post_thumbnail_cache();
+
+		$this->assertFalse( $GLOBALS['wp_query']->thumbnails_cached );
+
+		$this->factory->post->create_many( 3 );
+		$GLOBALS['wp_query'] = new WP_Query( array( 'post_type' => 'post' ) );
+
+		update_post_thumbnail_cache();
+
+		$this->assertTrue( $GLOBALS['wp_query']->thumbnails_cached );
+
+		$q = new WP_Query();
+		update_post_thumbnail_cache( $q );
+		$this->assertFalse( $q->thumbnails_cached );
+
+		$p = new WP_Query( array( 'post_type' => 'post' ) );
+		update_post_thumbnail_cache( $p );
+		$this->assertTrue( $p->thumbnails_cached );
+	}
+}