diff --git a/src/aphront/response/AphrontFileResponse.php b/src/aphront/response/AphrontFileResponse.php
--- a/src/aphront/response/AphrontFileResponse.php
+++ b/src/aphront/response/AphrontFileResponse.php
@@ -97,7 +97,12 @@
     if ($this->rangeMin || $this->rangeMax) {
       $len = $this->getContentLength();
       $min = $this->rangeMin;
+
       $max = $this->rangeMax;
+      if ($max === null) {
+        $max = ($len - 1);
+      }
+
       $headers[] = array('Content-Range', "bytes {$min}-{$max}/{$len}");
       $content_len = ($max - $min) + 1;
     } else {
diff --git a/src/applications/files/controller/PhabricatorFileDataController.php b/src/applications/files/controller/PhabricatorFileDataController.php
--- a/src/applications/files/controller/PhabricatorFileDataController.php
+++ b/src/applications/files/controller/PhabricatorFileDataController.php
@@ -64,14 +64,21 @@
     $range = $request->getHTTPHeader('range');
     if ($range) {
       $matches = null;
-      if (preg_match('/^bytes=(\d+)-(\d+)$/', $range, $matches)) {
+      if (preg_match('/^bytes=(\d+)-(\d*)$/', $range, $matches)) {
         // Note that the "Range" header specifies bytes differently than
         // we do internally: the range 0-1 has 2 bytes (byte 0 and byte 1).
         $begin = (int)$matches[1];
-        $end = (int)$matches[2] + 1;
+
+        // The "Range" may be "200-299" or "200-", meaning "until end of file".
+        if (strlen($matches[2])) {
+          $range_end = (int)$matches[2];
+          $end = $range_end + 1;
+        } else {
+          $range_end = null;
+        }
 
         $response->setHTTPResponseCode(206);
-        $response->setRange($begin, ($end - 1));
+        $response->setRange($begin, $range_end);
       }
     }
 
diff --git a/src/applications/files/format/__tests__/PhabricatorFileStorageFormatTestCase.php b/src/applications/files/format/__tests__/PhabricatorFileStorageFormatTestCase.php
--- a/src/applications/files/format/__tests__/PhabricatorFileStorageFormatTestCase.php
+++ b/src/applications/files/format/__tests__/PhabricatorFileStorageFormatTestCase.php
@@ -91,6 +91,14 @@
       $raw_data .= $data_chunk;
     }
     $this->assertEqual('cow jumped', $raw_data);
+
+    $iterator = $file->getFileDataIterator(4, null);
+    $raw_data = '';
+    foreach ($iterator as $data_chunk) {
+      $raw_data .= $data_chunk;
+    }
+    $this->assertEqual('cow jumped over the full moon.', $raw_data);
+
   }
 
   public function testStorageTampering() {