diff --git a/samples/Pdf/21a_Pdf.php b/samples/Pdf/21a_Pdf.php
index c4dc2c48..6ab1938f 100644
--- a/samples/Pdf/21a_Pdf.php
+++ b/samples/Pdf/21a_Pdf.php
@@ -25,7 +25,7 @@ background-color: yellow;
 
 EOF;
 
-    return preg_replace('@</head>@', "$newstyle</head>", $html);
+    return preg_replace('~</head>~', "$newstyle</head>", $html);
 }
 
 $helper->log('Write to Dompdf');