diff --git a/frappy/io.py b/frappy/io.py
index ba14e4f6..cddd5864 100644
--- a/frappy/io.py
+++ b/frappy/io.py
@@ -43,7 +43,7 @@ HEX_CODE = re.compile(r'[0-9a-fA-F][0-9a-fA-F]$')
 
 class HasIO(Module):
     """Mixin for modules using a communicator"""
-    io = Attached(mandatory=False)  # either io or uri must be given
+    io = Attached(Communicator, mandatory=False)  # either io or uri must be given
     uri = Property('uri for automatic creation of the attached communication module',
                    StringType(), default='')
 
diff --git a/frappy_psi/sea.py b/frappy_psi/sea.py
index fa17547f..b4a3b726 100644
--- a/frappy_psi/sea.py
+++ b/frappy_psi/sea.py
@@ -479,7 +479,7 @@ def pop_cfg(cfgdict, *args):
 
 
 class SeaModule(Module):
-    io = Attached()
+    io = Attached(SeaClient)
 
     # pylint: disable=too-many-statements,arguments-differ,too-many-branches
     def __new__(cls, name, logger, cfgdict, srv):