diff --git a/lib/spack/spack/util/multiproc.py b/lib/spack/spack/util/multiproc.py
index 91bac57c269..f465a3dbdc2 100644
--- a/lib/spack/spack/util/multiproc.py
+++ b/lib/spack/spack/util/multiproc.py
@@ -92,5 +92,5 @@ def wait(self):
         self.turnstile2.release()
 
 
-class BarrierTimeoutError:
+class BarrierTimeoutError(Exception):
     pass