diff --git a/src/python/jw/pkg/lib/init.py b/src/python/jw/pkg/lib/init.py
index 8098f687..014bdaed 100644
--- a/src/python/jw/pkg/lib/init.py
+++ b/src/python/jw/pkg/lib/init.py
@@ -6,16 +6,17 @@ from importlib import import_module
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
-    from collections.abc import MutableMapping
-    from typing import Any
+    from collections.abc import Iterable, MutableMapping
+    from typing import Any, Sequence
 
 def detect_modules(
     namespace: MutableMapping[str, Any],
     prefix: str | None = None,
     skip: set[str] | None = None,
     *,
+    base_types: Iterable[type[Any]] | None = None,
     extend_namespace: bool = True,
-) -> list[str]:
+) -> Sequence[str]:
 
     package_name = namespace.get("__name__")
     package_path = namespace.get("__path__")
@@ -41,7 +42,11 @@ def detect_modules(
             continue
 
         module = import_module(f".{module_name}", package_name)
-        cls = getattr(module, module_name)
+        cls = getattr(module, module_name, None)
+        if cls is None or not isinstance(cls, type):
+            continue
+        if base_types is not None and not issubclass(cls, tuple(base_types)):
+            continue
 
         namespace[module_name] = cls
         ret.append(module_name)