diff --git a/importlib_resources/readers.py b/importlib_resources/readers.py
index dc649cf..4f761c6 100644
--- a/importlib_resources/readers.py
+++ b/importlib_resources/readers.py
@@ -138,19 +138,23 @@ class NamespaceReader(abc.TraversableResources):
     def __init__(self, namespace_path):
         if 'NamespacePath' not in str(namespace_path):
             raise ValueError('Invalid path')
-        self.path = MultiplexedPath(*map(self._resolve, namespace_path))
+        self.path = MultiplexedPath(*filter(bool, map(self._resolve, namespace_path)))
 
     @classmethod
-    def _resolve(cls, path_str) -> abc.Traversable:
+    def _resolve(cls, path_str) -> abc.Traversable | None:
         r"""
         Given an item from a namespace path, resolve it to a Traversable.
 
         path_str might be a directory on the filesystem or a path to a
         zipfile plus the path within the zipfile, e.g. ``/foo/bar`` or
         ``/foo/baz.zip/inner_dir`` or ``foo\baz.zip\inner_dir\sub``.
+
+        path_str might also be a sentinel used by editable packages to
+        trigger other behaviors (see python/importlib_resources#311).
+        In that case, return None.
         """
-        (dir,) = (cand for cand in cls._candidate_paths(path_str) if cand.is_dir())
-        return dir
+        dirs = (cand for cand in cls._candidate_paths(path_str) if cand.is_dir())
+        return next(dirs, None)
 
     @classmethod
     def _candidate_paths(cls, path_str: str) -> Iterator[abc.Traversable]:
diff --git a/importlib_resources/tests/test_files.py b/importlib_resources/tests/test_files.py
index 311581c..f1fe233 100644
--- a/importlib_resources/tests/test_files.py
+++ b/importlib_resources/tests/test_files.py
@@ -60,6 +60,26 @@ class OpenZipTests(FilesTests, util.ZipSetup, unittest.TestCase):
 class OpenNamespaceTests(FilesTests, util.DiskSetup, unittest.TestCase):
     MODULE = 'namespacedata01'
 
+    def test_non_paths_in_dunder_path(self):
+        """
+        Non-path items in a namespace package's ``__path__`` are ignored.
+
+        As reported in python/importlib_resources#311, some tools
+        like Setuptools, when creating editable packages, will inject
+        non-paths into a namespace package's ``__path__``, a
+        sentinel like
+        ``__editable__.sample_namespace-1.0.finder.__path_hook__``
+        to cause the ``PathEntryFinder`` to be called when searching
+        for packages. In that case, resources should still be loadable.
+        """
+        import namespacedata01
+
+        namespacedata01.__path__.append(
+            '__editable__.sample_namespace-1.0.finder.__path_hook__'
+        )
+
+        resources.files(namespacedata01)
+
 
 class OpenNamespaceZipTests(FilesTests, util.ZipSetup, unittest.TestCase):
     ZIP_MODULE = 'namespacedata01'
diff --git a/newsfragments/311.bugfix.rst b/newsfragments/311.bugfix.rst
new file mode 100644
index 0000000..56655f7
--- /dev/null
+++ b/newsfragments/311.bugfix.rst
@@ -0,0 +1 @@
+Omit sentinel values from a namespace path.
\ No newline at end of file