diff --git a/wp-admin/includes/taxonomy.php b/wp-admin/includes/taxonomy.php
index 9769ea8c63..7423cf9214 100644
--- a/wp-admin/includes/taxonomy.php
+++ b/wp-admin/includes/taxonomy.php
@@ -117,7 +117,7 @@ function wp_insert_category($catarr, $wp_error = false) {
 	if ( $parent < 0 )
 		$parent = 0;
 
-	if ( empty($parent) || !category_exists( $parent ) || ($cat_ID && cat_is_ancestor_of($cat_ID, $parent) ) )
+	if ( empty( $parent ) || ! term_exists( $parent, $taxonomy ) || ( $cat_ID && term_is_ancestor_of( $cat_ID, $parent, $taxonomy ) ) )
 		$parent = 0;
 
 	$args = compact('name', 'slug', 'parent', 'description');
diff --git a/wp-includes/category.php b/wp-includes/category.php
index 4d02277417..96eefa8805 100644
--- a/wp-includes/category.php
+++ b/wp-includes/category.php
@@ -207,20 +207,9 @@ function get_cat_name( $cat_id ) {
  * @return bool Whether $cat2 is child of $cat1
  */
 function cat_is_ancestor_of( $cat1, $cat2 ) {
-	if ( ! isset($cat1->term_id) )
-		$cat1 = &get_category( $cat1 );
-	if ( ! isset($cat2->parent) )
-		$cat2 = &get_category( $cat2 );
-
-	if ( empty($cat1->term_id) || empty($cat2->parent) )
-		return false;
-	if ( $cat2->parent == $cat1->term_id )
-		return true;
-
-	return cat_is_ancestor_of( $cat1, get_category( $cat2->parent ) );
+	return term_is_ancestor_of( $cat1, $cat2, 'category' );
 }
 
-
 /**
  * Sanitizes category data based on context.
  *
@@ -235,7 +224,6 @@ function sanitize_category( $category, $context = 'display' ) {
 	return sanitize_term( $category, 'category', $context );
 }
 
-
 /**
  * Sanitizes data in single category key field.
  *
@@ -254,7 +242,6 @@ function sanitize_category_field( $field, $value, $cat_id, $context ) {
 
 /* Tags */
 
-
 /**
  * Retrieves all post tags.
  *
@@ -277,7 +264,6 @@ function &get_tags( $args = '' ) {
 	return $tags;
 }
 
-
 /**
  * Retrieve post tag by tag ID or tag object.
  *
@@ -301,10 +287,8 @@ function &get_tag( $tag, $output = OBJECT, $filter = 'raw' ) {
 	return get_term( $tag, 'post_tag', $output, $filter );
 }
 
-
 /* Cache */
 
-
 /**
  * Remove the category cache data based on ID.
  *
@@ -317,7 +301,6 @@ function clean_category_cache( $id ) {
 	clean_term_cache( $id, 'category' );
 }
 
-
 /**
  * Update category structure to old pre 2.3 from new taxonomy structure.
  *
@@ -355,5 +338,4 @@ function _make_cat_compat( &$category ) {
 	}
 }
 
-
 ?>
diff --git a/wp-includes/taxonomy.php b/wp-includes/taxonomy.php
index e6ec49ea52..2abb7c4cbb 100644
--- a/wp-includes/taxonomy.php
+++ b/wp-includes/taxonomy.php
@@ -1494,6 +1494,32 @@ function term_exists($term, $taxonomy = '', $parent = 0) {
 	return $wpdb->get_var( $wpdb->prepare("SELECT term_id FROM $wpdb->terms as t WHERE $else_where", $else_where_fields) );
 }
 
+/**
+ * Check if a term is an ancestor of another term.
+ *
+ * You can use either an id or the term object for both parameters.
+ *
+ * @since 3.4.0
+ *
+ * @param int|object $term1 ID or object to check if this is the parent term.
+ * @param int|object $term2 The child term.
+ * @param string $taxonomy Taxonomy name that $term1 and $term2 belong to.
+ * @return bool Whether $term2 is child of $term1
+ */
+function term_is_ancestor_of( $term1, $term2, $taxonomy ) {
+	if ( ! isset( $term1->term_id ) )
+		$term1 = get_term( $term1, $taxonomy );
+	if ( ! isset( $term2->parent ) )
+		$term2 = get_term( $term2, $taxonomy );
+
+	if ( empty( $term1->term_id ) || empty( $term2->parent ) )
+		return false;
+	if ( $term2->parent == $term1->term_id )
+		return true;
+
+	return term_is_ancestor_of( $term1, get_term( $term2->parent, $taxonomy ), $taxonomy );
+}
+
 /**
  * Sanitize Term all fields.
  *