diff --git a/src/wp-includes/class-wp-hook.php b/src/wp-includes/class-wp-hook.php
index 4796503dcc..b933a6e8eb 100644
--- a/src/wp-includes/class-wp-hook.php
+++ b/src/wp-includes/class-wp-hook.php
@@ -74,6 +74,10 @@ final class WP_Hook implements Iterator, ArrayAccess {
 	public function add_filter( $hook_name, $callback, $priority, $accepted_args ) {
 		$idx = _wp_filter_build_unique_id( $hook_name, $callback, $priority );
 
+		if ( ! is_int( $priority ) ) {
+			$priority = (string) $priority;
+		}
+
 		$priority_existed = isset( $this->callbacks[ $priority ] );
 
 		$this->callbacks[ $priority ][ $idx ] = array(