diff --git a/src/python/jw/pkg/lib/Cmd.py b/src/python/jw/pkg/lib/Cmd.py
index 51fea68f..dc7147ad 100644
--- a/src/python/jw/pkg/lib/Cmd.py
+++ b/src/python/jw/pkg/lib/Cmd.py
@@ -88,7 +88,15 @@ class AbstractCmd(abc.ABC):
         self, cmds: Cmd | list[Cmd] | Types[Any] | list[Types[Any]]
     ) -> None:
         if isinstance(cmds, Cmd):
-            raise NotImplementedError('Single Cmd should be handled elsewhere')
+            if any(child.name == cmds.name for child in self.__children):
+                raise Exception(
+                    f'Can\'t register subcommand with already taken name "{cmds.name}"'
+                )
+            self.__child_classes.append(type(cmds))
+            cmds.set_parent(self)
+            self.__children.append(cmds)
+            assert len(self.__children) == len(self.__child_classes)
+            return
         if isinstance(cmds, list):
             for cmd in cmds:
                 self.add_subcommands(cmd)