diff --git a/src/utils/PhutilSortVector.php b/src/utils/PhutilSortVector.php
--- a/src/utils/PhutilSortVector.php
+++ b/src/utils/PhutilSortVector.php
@@ -30,7 +30,7 @@
   }
 
   public function addString($value) {
-    if (strlen($value) && (strpos("\0", $value) !== false)) {
+    if (strlen($value) && (strpos($value, "\0") !== false)) {
       throw new Exception(
         pht(
           'String components of a sort vector must not contain NULL bytes.'));