diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index bf54055a241..a6f1cc50777 100644
--- a/lib/spack/spack/database.py
+++ b/lib/spack/spack/database.py
@@ -54,6 +54,7 @@
 from spack.version import Version
 from spack.spec import Spec
 from spack.error import SpackError
+from spack.packages import UnknownPackageError
 
 # DB goes in this directory underneath the root
 _db_dirname = '.spack-db'