diff --git a/src/docc/__init__.py b/src/docc/__init__.py
index d79c8eb..bd3546f 100644
--- a/src/docc/__init__.py
+++ b/src/docc/__init__.py
@@ -17,5 +17,5 @@
 The documentation compiler.
 """
 
-__version__ = "0.5.0"
+__version__ = "0.5.1"
 "Current version of docc"
diff --git a/src/docc/plugins/listing/__init__.py b/src/docc/plugins/listing/__init__.py
index b421194..f41adf5 100644
--- a/src/docc/plugins/listing/__init__.py
+++ b/src/docc/plugins/listing/__init__.py
@@ -111,6 +111,11 @@ class ListingDiscover(Discover):
     def __init__(self, config: PluginSettings) -> None:
         pass
 
+    def _listing_source(
+        self, source: Source, parent: PurePath
+    ) -> "ListingSource":
+        return ListingSource(parent, parent / "index", set())
+
     def discover(self, known: FrozenSet[T]) -> Iterator["ListingSource"]:
         """
         Find sources.
@@ -129,7 +134,7 @@ def discover(self, known: FrozenSet[T]) -> Iterator["ListingSource"]:
                 try:
                     listing = listings[parent]
                 except KeyError:
-                    listing = ListingSource(parent, parent / "index", set())
+                    listing = self._listing_source(source, parent)
                     listings[parent] = listing
                     yield listing