--- a/tincan.py	Wed May 15 00:16:06 2019 -0700
+++ b/tincan.py	Thu May 16 11:42:56 2019 -0700
@@ -466,8 +466,8 @@
         self._class = None
         for i in dir(mod):
             v = getattr(mod, i)
-            if isclass(v) and issubclass(v, klass):
-                if self._class is not None:
+            if isclass(v) and issubclass(v, klass) and v is not klass:
+                if self._class is not None and self._class is not klass:
                     raise TinCanError("{0}: contains multiple {1} classes".format(pypath, klass.__name__))
                 self._class = v
         if self._class is None: