diff -r 1b145e8ae4be Lib/selectors.py
--- a/Lib/selectors.py	Sun Jan 11 15:51:11 2015 -0500
+++ b/Lib/selectors.py	Mon Jan 12 12:01:59 2015 +0100
@@ -174,6 +174,8 @@ class BaseSelector(metaclass=ABCMeta):
         SelectorKey for this file object
         """
         mapping = self.get_map()
+        if mapping is None:
+            raise RuntimeError('Selector is closed')
         try:
             return mapping[fileobj]
         except KeyError:
@@ -256,6 +258,7 @@ class _BaseSelectorImpl(BaseSelector):
 
     def close(self):
         self._fd_to_key.clear()
+        self._map = None
 
     def get_map(self):
         return self._map
diff -r 1b145e8ae4be Lib/test/test_selectors.py
--- a/Lib/test/test_selectors.py	Sun Jan 11 15:51:11 2015 -0500
+++ b/Lib/test/test_selectors.py	Mon Jan 12 12:01:59 2015 +0100
@@ -180,14 +180,17 @@ class BaseSelectorTestCase(unittest.Test
         s = self.SELECTOR()
         self.addCleanup(s.close)
 
+        mapping = s.get_map()
         rd, wr = self.make_socketpair()
 
         s.register(rd, selectors.EVENT_READ)
         s.register(wr, selectors.EVENT_WRITE)
 
         s.close()
-        self.assertRaises(KeyError, s.get_key, rd)
-        self.assertRaises(KeyError, s.get_key, wr)
+        self.assertRaises(RuntimeError, s.get_key, rd)
+        self.assertRaises(RuntimeError, s.get_key, wr)
+        self.assertRaises(KeyError, mapping.__getitem__, rd)
+        self.assertRaises(KeyError, mapping.__getitem__, wr)
 
     def test_get_key(self):
         s = self.SELECTOR()
@@ -254,8 +257,8 @@ class BaseSelectorTestCase(unittest.Test
             sel.register(rd, selectors.EVENT_READ)
             sel.register(wr, selectors.EVENT_WRITE)
 
-        self.assertRaises(KeyError, s.get_key, rd)
-        self.assertRaises(KeyError, s.get_key, wr)
+        self.assertRaises(RuntimeError, s.get_key, rd)
+        self.assertRaises(RuntimeError, s.get_key, wr)
 
     def test_fileno(self):
         s = self.SELECTOR()