diff --git a/wp-includes/category-template.php b/wp-includes/category-template.php
index ba3f18fe70..cceac1aef7 100644
--- a/wp-includes/category-template.php
+++ b/wp-includes/category-template.php
@@ -182,14 +182,17 @@ function get_the_category_list($separator = '', $parents='', $post_id = false) {
 function in_category( $category ) { // Check if the current post is in the given category
 	global $post;
 
+	if ( empty($category) )
+		return false;
+
 	$cat_ID = get_cat_ID($category);
-	if (0 != $cat_ID)
+	if ( $cat_ID )
 		$category = $cat_ID;
 
 	$categories = get_object_term_cache($post->ID, 'category');
 	if ( false === $categories )
 		$categories = wp_get_object_terms($post->ID, 'category');
-	if(array_key_exists($category, $categories))
+	if ( array_key_exists($category, $categories) )
 		return true;
 	else
 		return false;