diff -r ba72da4883eb Lib/importlib/_bootstrap.py
--- a/Lib/importlib/_bootstrap.py	Mon Dec 01 13:07:45 2014 +0200
+++ b/Lib/importlib/_bootstrap.py	Mon Dec 01 16:57:44 2014 -0500
@@ -453,11 +453,11 @@
     else:
         suffixes = OPTIMIZED_BYTECODE_SUFFIXES
     head, tail = _path_split(path)
-    base_filename, sep, _ = tail.partition('.')
+    base, sep, rest = tail.rpartition('.')
     tag = sys.implementation.cache_tag
     if tag is None:
         raise NotImplementedError('sys.implementation.cache_tag is None')
-    filename = ''.join([base_filename, sep, tag, suffixes[0]])
+    filename = ''.join([(base if base else rest), sep, tag, suffixes[0]])
     return _path_join(head, _PYCACHE, filename)
 
 
diff -r ba72da4883eb Lib/test/test_py_compile.py
--- a/Lib/test/test_py_compile.py	Mon Dec 01 13:07:45 2014 +0200
+++ b/Lib/test/test_py_compile.py	Mon Dec 01 16:57:44 2014 -0500
@@ -99,5 +99,21 @@
         self.assertFalse(os.path.exists(
             importlib.util.cache_from_source(bad_coding)))
 
+    def test_double_dot_no_clobber(self):
+        # http://bugs.python.org/issue22966
+        # py_compile foo.bar.py -> __pycache__/foo.cpython-34.pyc
+        weird_path = os.path.join(self.directory, 'foo.bar.py')
+        cache_path = importlib.util.cache_from_source(weird_path)
+        pyc_path = weird_path + 'c'
+        self.assertEqual(
+            '/'.join(cache_path.split('/')[-2:]),
+            '__pycache__/foo.bar.cpython-34.pyc')
+        with open(weird_path, 'w') as file:
+            file.write('x = 123\n')
+        py_compile.compile(weird_path)
+        self.assertTrue(os.path.exists(cache_path))
+        self.assertFalse(os.path.exists(pyc_path))
+
+
 if __name__ == "__main__":
     unittest.main()