diff --git a/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
index c69a06bd9a..5d446d4fbb 100644
--- a/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
@@ -1,76 +1,96 @@
 <?php
 
 final class DifferentialCreateRawDiffConduitAPIMethod
   extends DifferentialConduitAPIMethod {
 
   public function getAPIMethodName() {
     return 'differential.createrawdiff';
   }
 
   public function getMethodDescription() {
     return pht('Create a new Differential diff from a raw diff source.');
   }
 
   protected function defineParamTypes() {
     return array(
       'diff' => 'required string',
       'repositoryPHID' => 'optional string',
       'viewPolicy' => 'optional string',
     );
   }
 
   protected function defineReturnType() {
     return 'nonempty dict';
   }
 
   protected function execute(ConduitAPIRequest $request) {
     $viewer = $request->getUser();
     $raw_diff = $request->getValue('diff');
 
     $repository_phid = $request->getValue('repositoryPHID');
     if ($repository_phid) {
       $repository = id(new PhabricatorRepositoryQuery())
         ->setViewer($viewer)
         ->withPHIDs(array($repository_phid))
         ->executeOne();
       if (!$repository) {
         throw new Exception(
           pht('No such repository "%s"!', $repository_phid));
       }
     }
 
     $parser = new ArcanistDiffParser();
     $changes = $parser->parseDiff($raw_diff);
     $diff = DifferentialDiff::newFromRawChanges($viewer, $changes);
 
+    // We're bounded by doing INSERTs for all the hunks and changesets, so
+    // estimate the number of inserts we'll require.
+    $size = 0;
+    foreach ($diff->getChangesets() as $changeset) {
+      $hunks = $changeset->getHunks();
+      $size += 1 + count($hunks);
+    }
+
+    $raw_limit = 10000;
+    if ($size > $raw_limit) {
+      throw new Exception(
+        pht(
+          'The raw diff you have submitted is too large to parse (it affects '.
+          'more than %s paths and hunks). Differential should only be used '.
+          'for changes which are small enough to receive detailed human '.
+          'review. See "Differential User Guide: Large Changes" in the '.
+          'documentation for more information.',
+          new PhutilNumber($raw_limit)));
+    }
+
     $diff_data_dict = array(
       'creationMethod' => 'web',
       'authorPHID' => $viewer->getPHID(),
       'repositoryPHID' => $repository_phid,
       'lintStatus' => DifferentialLintStatus::LINT_SKIP,
       'unitStatus' => DifferentialUnitStatus::UNIT_SKIP,
     );
 
     $xactions = array(
       id(new DifferentialTransaction())
         ->setTransactionType(DifferentialDiffTransaction::TYPE_DIFF_CREATE)
         ->setNewValue($diff_data_dict),
     );
 
     if ($request->getValue('viewPolicy')) {
       $xactions[] = id(new DifferentialTransaction())
         ->setTransactionType(PhabricatorTransactions::TYPE_VIEW_POLICY)
         ->setNewValue($request->getValue('viewPolicy'));
     }
 
     id(new DifferentialDiffEditor())
       ->setActor($viewer)
       ->setContentSourceFromConduitRequest($request)
       ->setContinueOnNoEffect(true)
       ->setLookupRepository(false) // respect user choice
       ->applyTransactions($diff, $xactions);
 
     return $this->buildDiffInfoDictionary($diff);
   }
 
 }
diff --git a/src/applications/files/exception/PhabricatorFileUploadException.php b/src/applications/files/exception/PhabricatorFileUploadException.php
index 095565793f..388e52411c 100644
--- a/src/applications/files/exception/PhabricatorFileUploadException.php
+++ b/src/applications/files/exception/PhabricatorFileUploadException.php
@@ -1,29 +1,32 @@
 <?php
 
 final class PhabricatorFileUploadException extends Exception {
 
   public function __construct($code) {
     $map = array(
-      'UPLOAD_ERR_INI_SIZE' => pht(
+      UPLOAD_ERR_INI_SIZE => pht(
         "Uploaded file is too large: current limit is %s. To adjust ".
         "this limit change '%s' in php.ini.",
         ini_get('upload_max_filesize'),
         'upload_max_filesize'),
-      'UPLOAD_ERR_FORM_SIZE' => pht(
+      UPLOAD_ERR_FORM_SIZE => pht(
         'File is too large.'),
-      'UPLOAD_ERR_PARTIAL' => pht(
+      UPLOAD_ERR_PARTIAL => pht(
         'File was only partially transferred, upload did not complete.'),
-      'UPLOAD_ERR_NO_FILE' => pht(
+      UPLOAD_ERR_NO_FILE => pht(
         'No file was uploaded.'),
-      'UPLOAD_ERR_NO_TMP_DIR' => pht(
+      UPLOAD_ERR_NO_TMP_DIR => pht(
         'Unable to write file: temporary directory does not exist.'),
-      'UPLOAD_ERR_CANT_WRITE' => pht(
+      UPLOAD_ERR_CANT_WRITE => pht(
         'Unable to write file: failed to write to temporary directory.'),
-      'UPLOAD_ERR_EXTENSION' => pht(
+      UPLOAD_ERR_EXTENSION => pht(
         'Unable to upload: a PHP extension stopped the upload.'),
     );
 
-    $message = idx($map, $code, pht('Upload failed: unknown error.'));
+    $message = idx(
+      $map,
+      $code,
+      pht('Upload failed: unknown error (%s).', $code));
     parent::__construct($message, $code);
   }
 }