diff --git a/src/xsprintf/xsprintf.php b/src/xsprintf/xsprintf.php
--- a/src/xsprintf/xsprintf.php
+++ b/src/xsprintf/xsprintf.php
@@ -1,5 +1,7 @@
 <?php

+setlocale(LC_CTYPE, "en_US.UTF-8");
+
 /**
  * Parse a `sprintf()`-style format string in an extensible way.
  *