diff --git a/src/wp-includes/category-template.php b/src/wp-includes/category-template.php
index 27b8bf221f..57f7cb9ada 100644
--- a/src/wp-includes/category-template.php
+++ b/src/wp-includes/category-template.php
@@ -232,6 +232,9 @@ function get_the_category_list( $separator = '', $parents='', $post_id = false )
  * @return bool True if the current post is in any of the given categories.
  */
 function in_category( $category, $post = null ) {
+	if ( empty( $category ) )
+		return false;
+
 	return has_category( $category, $post );
 }
 
diff --git a/tests/phpunit/tests/taxonomy.php b/tests/phpunit/tests/taxonomy.php
index c9c6ee6fcc..e94ad4c4f3 100644
--- a/tests/phpunit/tests/taxonomy.php
+++ b/tests/phpunit/tests/taxonomy.php
@@ -152,4 +152,20 @@ class Tests_Taxonomy extends WP_UnitTestCase {
 		_unregister_post_type( $post_type );
 
 	}
+	/**
+	 * @ticket 25706
+	 */
+	function test_in_category() {
+		$post = $this->factory->post->create_and_get();
+
+		// in_category() returns false when first parameter is empty()
+		$this->assertFalse( in_category( '', $post ) );
+		$this->assertFalse( in_category( false, $post ) );
+		$this->assertFalse( in_category( null, $post ) );
+
+		// Test expected behavior of in_category()
+		$term = wp_insert_term( 'Test', 'category' );
+		wp_set_object_terms( $post->ID, $term['term_id'], 'category' );
+		$this->assertTrue( in_category( $term['term_id'], $post ) );
+	}
 }