diff --git a/src/parser/PhutilJSON.php b/src/parser/PhutilJSON.php
--- a/src/parser/PhutilJSON.php
+++ b/src/parser/PhutilJSON.php
@@ -131,7 +131,8 @@
       return $this->encodeFormattedObject($value, $depth);
     } else {
       if (defined('JSON_UNESCAPED_SLASHES')) {
-        // If we have a new enough version of PHP, disable escaping of slashes
+        // If we have PHP >= 5.4.0 && the JSON extension is installed (as of
+        // PHP 8.0.0, it is a core PHP extension), disable escaping of slashes
         // when pretty-printing values. Escaping slashes can defuse an attack
         // where the attacker embeds "</script>" inside a JSON string, but that
         // isn't relevant when rendering JSON for human viewers.