diff --git a/src/applications/files/conduit/FileUploadChunkConduitAPIMethod.php b/src/applications/files/conduit/FileUploadChunkConduitAPIMethod.php
index 949bdde28a..b4d1a23a3f 100644
--- a/src/applications/files/conduit/FileUploadChunkConduitAPIMethod.php
+++ b/src/applications/files/conduit/FileUploadChunkConduitAPIMethod.php
@@ -61,15 +61,20 @@ final class FileUploadChunkConduitAPIMethod
       $mime_type = 'application/octet-stream';
     }
 
+    $params = array(
+      'name' => $file->getMonogram().'.chunk-'.$chunk->getID(),
+      'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
+    );
+
+    if ($mime_type !== null) {
+      $params['mime-type'] = 'application/octet-stream';
+    }
+
     // NOTE: These files have a view policy which prevents normal access. They
     // are only accessed through the storage engine.
     $chunk_data = PhabricatorFile::newFromFileData(
       $data,
-      array(
-        'name' => $file->getMonogram().'.chunk-'.$chunk->getID(),
-        'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
-        'mime-type' => $mime_type,
-      ));
+      $params);
 
     $chunk->setDataFilePHID($chunk_data->getPHID())->save();
 
diff --git a/src/applications/files/storage/PhabricatorFile.php b/src/applications/files/storage/PhabricatorFile.php
index 4faecbd557..db15fb43e0 100644
--- a/src/applications/files/storage/PhabricatorFile.php
+++ b/src/applications/files/storage/PhabricatorFile.php
@@ -251,6 +251,11 @@ final class PhabricatorFile extends PhabricatorFileDAO
     $file->setMimeType('application/octet-stream');
 
     $chunked_hash = idx($params, 'chunkedHash');
+
+    // Get rid of this parameter now; we aren't passing it any further down
+    // the stack.
+    unset($params['chunkedHash']);
+
     if ($chunked_hash) {
       $file->setContentHash($chunked_hash);
     } else {