diff --git a/CHANGES.rst b/CHANGES.rst
index 290694e..1055a2f 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,3 +1,9 @@
+v5.7.1
+======
+
+* #249: In ``simple.ResourceContainer.joinpath``, honor
+  names split by ``posixpath.sep``.
+
 v5.7.0
 ======
 
diff --git a/importlib_resources/simple.py b/importlib_resources/simple.py
index 1f6e43a..d0fbf23 100644
--- a/importlib_resources/simple.py
+++ b/importlib_resources/simple.py
@@ -99,13 +99,19 @@ def iterdir(self):
     def open(self, *args, **kwargs):
         raise IsADirectoryError()
 
-    def joinpath(self, *names):
-        if not names:
+    @staticmethod
+    def _flatten(compound_names):
+        for name in compound_names:
+            yield from name.split('/')
+
+    def joinpath(self, *descendants):
+        if not descendants:
             return self
-        name, rest = names[0], names[1:]
+        names = self._flatten(descendants)
+        target = next(names)
         return next(
-            traversable for traversable in self.iterdir() if traversable.name == name
-        ).joinpath(*rest)
+            traversable for traversable in self.iterdir() if traversable.name == target
+        ).joinpath(*names)
 
 
 class TraversableReader(TraversableResources, SimpleReader):