diff --git a/src/Escaper/AbstractEscaper.php b/src/Escaper/AbstractEscaper.php
index fc4f816..ddc760a 100644
--- a/src/Escaper/AbstractEscaper.php
+++ b/src/Escaper/AbstractEscaper.php
@@ -110,11 +110,13 @@ public function getEncoding()
      *
      * @param string $regex The regex to determine what characters to replace.
      *
-     * @return mixed The escaped value.
+     * @return string The escaped value.
      *
      */
     protected function replace($raw, $regex)
     {
+        $raw = (string) $raw;
+
         // pre-empt replacement
         if ($raw === '' || ctype_digit($raw)) {
             return $raw;
diff --git a/src/Escaper/HtmlEscaper.php b/src/Escaper/HtmlEscaper.php
index 4642e99..c05e98e 100644
--- a/src/Escaper/HtmlEscaper.php
+++ b/src/Escaper/HtmlEscaper.php
@@ -59,11 +59,13 @@ public function __construct($flags = null, $encoding = null)
      *
      * @param mixed $raw The value to be escaped.
      *
-     * @return mixed The escaped value.
+     * @return string The escaped value.
      *
      */
     public function __invoke($raw)
     {
+        $raw = (string) $raw;
+
         // pre-empt escaping
         if ($raw === '' || ctype_digit($raw)) {
             return $raw;