diff --git a/src/allmydata/immutable/checker.py b/src/allmydata/immutable/checker.py
index a4c95afb3..b8642c35d 100644
--- a/src/allmydata/immutable/checker.py
+++ b/src/allmydata/immutable/checker.py
@@ -1,11 +1,10 @@
 from foolscap.api import DeadReferenceError, RemoteException
-from twisted.internet import defer
 from allmydata.hashtree import IncompleteHashTree
 from allmydata.check_results import CheckResults
 from allmydata.immutable import download
 from allmydata.uri import CHKFileVerifierURI
 from allmydata.util.assertutil import precondition
-from allmydata.util import base32, deferredutil, dictutil, log
+from allmydata.util import base32, idlib, deferredutil, dictutil, log
 from allmydata.util.hashutil import file_renewal_secret_hash, \
      file_cancel_secret_hash, bucket_renewal_secret_hash, \
      bucket_cancel_secret_hash