diff --git a/wp-admin/includes/class-walker-category-checklist.php b/wp-admin/includes/class-walker-category-checklist.php
index f4d3fbed36..4c6cc9ef31 100644
--- a/wp-admin/includes/class-walker-category-checklist.php
+++ b/wp-admin/includes/class-walker-category-checklist.php
@@ -81,11 +81,11 @@ class Walker_Category_Checklist extends Walker {
 			$name = 'tax_input[' . $taxonomy . ']';
 		}
 
-		$args['popular_cats'] = empty( $args['popular_cats'] ) ? array() : $args['popular_cats'];
+		$args['popular_cats'] = ! empty( $args['popular_cats'] ) ? array_map( 'intval', $args['popular_cats'] ) : array();
 
 		$class = in_array( $category->term_id, $args['popular_cats'], true ) ? ' class="popular-category"' : '';
 
-		$args['selected_cats'] = empty( $args['selected_cats'] ) ? array() : $args['selected_cats'];
+		$args['selected_cats'] = ! empty( $args['selected_cats'] ) ? array_map( 'intval', $args['selected_cats'] ) : array();
 
 		if ( ! empty( $args['list_only'] ) ) {
 			$aria_checked = 'false';
diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index d77d2104da..ad87a89521 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -120,7 +120,7 @@ function wp_terms_checklist( $post_id = 0, $args = array() ) {
 	$args['list_only'] = ! empty( $parsed_args['list_only'] );
 
 	if ( is_array( $parsed_args['selected_cats'] ) ) {
-		$args['selected_cats'] = $parsed_args['selected_cats'];
+		$args['selected_cats'] = array_map( 'intval', $parsed_args['selected_cats'] );
 	} elseif ( $post_id ) {
 		$args['selected_cats'] = wp_get_object_terms( $post_id, $taxonomy, array_merge( $args, array( 'fields' => 'ids' ) ) );
 	} else {
@@ -128,7 +128,7 @@ function wp_terms_checklist( $post_id = 0, $args = array() ) {
 	}
 
 	if ( is_array( $parsed_args['popular_cats'] ) ) {
-		$args['popular_cats'] = $parsed_args['popular_cats'];
+		$args['popular_cats'] = array_map( 'intval', $parsed_args['popular_cats'] );
 	} else {
 		$args['popular_cats'] = get_terms(
 			array(
diff --git a/wp-includes/version.php b/wp-includes/version.php
index d7b2cb2d4d..7a2fe6daca 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-48878';
+$wp_version = '5.6-alpha-48880';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.