diff --git a/python/obitools3/dms/column/column.pyx b/python/obitools3/dms/column/column.pyx
index 50a3311..f060ea4 100644
--- a/python/obitools3/dms/column/column.pyx
+++ b/python/obitools3/dms/column/column.pyx
@@ -350,8 +350,7 @@ cdef register_column_class(obitype_t obitype,
 
 cdef register_all_column_classes() :
     
-    #obi3 = importlib.import_module("obitools3")
-    x = list(pkgutil.walk_packages(typed_column.__path__))   # TODO restrain the walking
+    x = list(pkgutil.walk_packages(typed_column.__path__, prefix="obitools3.dms.column.typed_column."))
     all_modules = [importlib.import_module(a[1]) for a in x]
     for mod in all_modules :
         getattr(mod, 'register_class')()