diff --git a/scripts/phutil_symbols.php b/scripts/phutil_symbols.php
--- a/scripts/phutil_symbols.php
+++ b/scripts/phutil_symbols.php
@@ -531,6 +531,15 @@
       'self'   => true,
 
       'PhutilBootloader' => true,
+
+      // PHP7 defines these new parent classes of "Exception", but they do not
+      // exist prior to PHP7. It's possible to use them safely in PHP5, in
+      // some cases, to write code which is compatible with either PHP5 or
+      // PHP7, but it s hard for us tell if a particular use is safe or not.
+      // For now, assume users know what they're doing and that uses are safe.
+      // For discussion, see T12855.
+      'Throwable' => true,
+      'Error' => true,
     ),
     'function'  => array_filter(
       array(