diff --git a/src/future/http/status/HTTPFutureHTTPResponseStatus.php b/src/future/http/status/HTTPFutureHTTPResponseStatus.php
--- a/src/future/http/status/HTTPFutureHTTPResponseStatus.php
+++ b/src/future/http/status/HTTPFutureHTTPResponseStatus.php
@@ -13,7 +13,7 @@
 
     // NOTE: Avoiding PhutilUTF8StringTruncator here because this isn't lazy
     // and responses may be large.
-    if (strlen($body) > 512) {
+    if ($body !== null && strlen($body) > 512) {
       $excerpt = substr($body, 0, 512).'...';
     } else {
       $excerpt = $body;