diff --git a/src/JsonSchema/Constraints/FormatConstraint.php b/src/JsonSchema/Constraints/FormatConstraint.php
index 7bc059c2..a55356d1 100644
--- a/src/JsonSchema/Constraints/FormatConstraint.php
+++ b/src/JsonSchema/Constraints/FormatConstraint.php
@@ -197,7 +197,7 @@ protected function validateDateTime($datetime, $format)
 
     protected function validateRegex($regex)
     {
-        return false !== @preg_match('/' . $regex . '/u', '');
+        return false !== @preg_match('#' . str_replace('#', '\\#', $regex) . '#u', '');
     }
 
     protected function validateColor($color)