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
@@ -21,7 +21,8 @@
 
     $content_type = BaseHTTPFuture::getHeader($headers, 'Content-Type');
     $match = null;
-    if (preg_match('/;\s*charset=([^;]+)/', $content_type, $match)) {
+    if ($content_type !== null && strlen($content_type)
+      && preg_match('/;\s*charset=([^;]+)/', $content_type, $match)) {
       $encoding = trim($match[1], "\"'");
       try {
         $excerpt = phutil_utf8_convert($excerpt, 'UTF-8', $encoding);
diff --git a/src/parser/ArcanistDiffParser.php b/src/parser/ArcanistDiffParser.php
--- a/src/parser/ArcanistDiffParser.php
+++ b/src/parser/ArcanistDiffParser.php
@@ -263,7 +263,7 @@
         // searching for "diff -r" or "diff --git" in the text.
         $this->saveLine();
         $line = $this->nextLineThatLooksLikeDiffStart();
-        if (!$this->tryMatchHeader($patterns, $line, $match)) {
+        if ($line === null || !$this->tryMatchHeader($patterns, $line, $match)) {
           // Restore line before guessing to display correct error.
           $this->restoreLine();
           $failed_parse = true;