diff --git a/src/unit/engine/phutil/ArcanistPhutilTestCase.php b/src/unit/engine/phutil/ArcanistPhutilTestCase.php
index 291cdcbc..761323f6 100644
--- a/src/unit/engine/phutil/ArcanistPhutilTestCase.php
+++ b/src/unit/engine/phutil/ArcanistPhutilTestCase.php
@@ -576,6 +576,8 @@ abstract class ArcanistPhutilTestCase {
           // TODO: This indicates "unreachable", but it flags the closing braces
           // of functions which end in "return", which is super ridiculous. Just
           // ignore it for now.
+          //
+          // See http://bugs.xdebug.org/view.php?id=1041
           $str .= 'N'; // Not executable.
         } else if ($c === 1) {
           $str .= 'C'; // Covered.