diff --git a/python/obitools3/dms/column/column.pyx b/python/obitools3/dms/column/column.pyx
index 7f46806..50a3311 100644
--- a/python/obitools3/dms/column/column.pyx
+++ b/python/obitools3/dms/column/column.pyx
@@ -1,4 +1,5 @@
 #cython: language_level=3
+from obitools3.dms.column import typed_column
  
 
 __OBIDMS_COLUMN_CLASS__ = {}
@@ -24,6 +25,8 @@ from obitools3.utils cimport tobytes, \
                              bytes2str, \
                              str2bytes
  
+from obitools3.dms.column import typed_column
+ 
 import importlib
 import inspect
 import pkgutil
@@ -348,8 +351,8 @@ cdef register_column_class(obitype_t obitype,
 cdef register_all_column_classes() :
     
     #obi3 = importlib.import_module("obitools3")
-    x = list(pkgutil.walk_packages())   # TODO restrain the walking
-    all_modules = [importlib.import_module(a[1]) for a in x if a[1].startswith("obitools3.dms.column.typed_column.")]
+    x = list(pkgutil.walk_packages(typed_column.__path__))   # TODO restrain the walking
+    all_modules = [importlib.import_module(a[1]) for a in x]
     for mod in all_modules :
         getattr(mod, 'register_class')()