diff --git a/festim/__init__.py b/festim/__init__.py
index ca22327fe..de4a2652c 100644
--- a/festim/__init__.py
+++ b/festim/__init__.py
@@ -21,4 +21,7 @@
 
 from .species import Species, Trap
 
+from .subdomain.surface_subdomain import SurfaceSubdomain1D
+from .subdomain.volume_subdomain import VolumeSubdomain1D
+
 from .hydrogen_transport_problem import HydrogenTransportProblem