1 files changed, 15 insertions, 1 deletions
diff --git a/setuptools/monkey.py b/setuptools/monkey.py
index 94f22a56..6d3711ec 100644
--- a/setuptools/monkey.py
+++ b/setuptools/monkey.py
@@ -21,6 +21,20 @@ if you think you need this functionality.
 """
 
 
+def _get_mro(cls):
+    """
+    Returns the bases classes for cls sorted by the MRO.
+
+    Works around an issue on Jython where inspect.getmro will not return all
+    base classes if multiple classes share the same name. Instead, this
+    function will return a tuple containing the class itself, and the contents
+    of cls.__bases__. See https://github.com/pypa/setuptools/issues/1024.
+    """
+    if platform.python_implementation() == "Jython":
+        return (cls,) + cls.__bases__
+    return inspect.getmro(cls)
+
+
 def get_unpatched(item):
     lookup = (
         get_unpatched_class if isinstance(item, six.class_types) else
@@ -38,7 +52,7 @@ def get_unpatched_class(cls):
     """
     external_bases = (
         cls
-        for cls in inspect.getmro(cls)
+        for cls in _get_mro(cls)
         if not cls.__module__.startswith('setuptools')
     )
     base = next(external_bases)