diff --git wp-includes/taxonomy.php wp-includes/taxonomy.php
index 410e762..f37c695 100644
--- wp-includes/taxonomy.php
+++ wp-includes/taxonomy.php
@@ -220,6 +220,9 @@ function get_taxonomy( $taxonomy ) {
 function taxonomy_exists( $taxonomy ) {
 	global $wp_taxonomies;
 
+    if (! is_string($taxonomy))
+        _doing_it_wrong(__FUNCTION__, 'This function will only accept a string as a parameter.', '3.9');
+
 	return isset( $wp_taxonomies[$taxonomy] );
 }
 
@@ -3405,4 +3408,4 @@ function wp_check_term_hierarchy_for_loops( $parent, $term_id, $taxonomy ) {
 		wp_update_term( $loop_member, $taxonomy, array( 'parent' => 0 ) );
 
 	return $parent;
-}
\ No newline at end of file
+}