diff --git a/project.py b/project.py
index d07b521..023cf73 100644
--- a/project.py
+++ b/project.py
@@ -2327,8 +2327,8 @@
         path = os.path.join(self._project.worktree, '.git', HEAD)
       try:
         fd = open(path, 'rb')
-      except IOError:
-        raise NoManifestException(path)
+      except IOError as e:
+        raise NoManifestException(path, str(e))
       try:
         line = fd.read()
       finally: