diff --git a/error.py b/error.py
index cb3b725..5238158 100644
--- a/error.py
+++ b/error.py
@@ -75,3 +75,10 @@
   """
   def __init__(self, extra_args=[]):
     self.extra_args = extra_args
+
+class HookError(Exception):
+  """Thrown if a 'repo-hook' could not be run.
+
+  The common case is that the file wasn't present when we tried to run it.
+  """
+  pass