diff --git a/ognibuild/session/__init__.py b/ognibuild/session/__init__.py
index 320cd64..801c125 100644
--- a/ognibuild/session/__init__.py
+++ b/ognibuild/session/__init__.py
@@ -100,6 +100,8 @@ class Session(object):
     def external_path(self, path: str) -> str:
         raise NotImplementedError
 
+    is_temporary: bool
+
 
 class SessionSetupFailure(Exception):
     """Session failed to be set up."""
diff --git a/ognibuild/session/plain.py b/ognibuild/session/plain.py
index c7507f1..8d9de34 100644
--- a/ognibuild/session/plain.py
+++ b/ognibuild/session/plain.py
@@ -112,3 +112,5 @@ class PlainSession(Session):
 
     def setup_from_directory(self, path):
         return path, path
+
+    is_temporary = False
diff --git a/ognibuild/session/schroot.py b/ognibuild/session/schroot.py
index 2faeeb6..10fc9ca 100644
--- a/ognibuild/session/schroot.py
+++ b/ognibuild/session/schroot.py
@@ -215,3 +215,5 @@ class SchrootSession(Session):
         export_directory = os.path.join(directory, subdir)
         shutil.copytree(path, export_directory, dirs_exist_ok=True)
         return export_directory, os.path.join(reldir, subdir)
+
+    is_temporary = True