diff --git a/src/repository/api/ArcanistMercurialAPI.php b/src/repository/api/ArcanistMercurialAPI.php
--- a/src/repository/api/ArcanistMercurialAPI.php
+++ b/src/repository/api/ArcanistMercurialAPI.php
@@ -464,6 +464,16 @@
     // on a large repo) because mercurial has to decompress and parse the
     // entire manifest every time. Do it in one large batch instead.
 
+    // See T6112. On windows escapeshellarg removes the %-sign from the command
+    // string rendering the fast approach useless.
+    if (phutil_is_windows()) {
+      $filedata = array();
+      foreach ($paths as $path) {
+        $filedata[$path] = $this->getFileDataAtRevision($path, $revision);
+      }
+      return $filedata;
+    }
+
     // hg cat will write the file data to files in a temp directory
     $tmpdir = Filesystem::createTemporaryDirectory();