diff -r f4c6dab59cd8 Lib/unittest/loader.py
--- a/Lib/unittest/loader.py	Tue Apr 26 17:04:18 2016 +0200
+++ b/Lib/unittest/loader.py	Fri Apr 29 09:48:20 2016 +0200
@@ -35,6 +35,14 @@
         return testFailure
 
 
+def ispackage(path):
+    """Guess whether a path refers to a package directory."""
+    if os.path.isdir(path):
+        for ext in ('.py', '.pyc'):
+            if os.path.isfile(os.path.join(path, '__init__' + ext)):
+                return True
+    return False
+
 def _make_failed_import_test(name, suiteClass):
     message = 'Failed to import test module: %s\n%s' % (
         name, traceback.format_exc())
@@ -283,7 +291,7 @@
         if os.path.isdir(os.path.abspath(start_dir)):
             start_dir = os.path.abspath(start_dir)
             if start_dir != top_level_dir:
-                is_not_importable = not os.path.isfile(os.path.join(start_dir, '__init__.py'))
+                is_not_importable = not ispackage(start_dir)
         else:
             # support for discovery from dotted module names
             try:
@@ -451,8 +459,7 @@
                         msg % (mod_name, module_dir, expected_dir))
                 return self.loadTestsFromModule(module, pattern=pattern), False
         elif os.path.isdir(full_path):
-            if (not namespace and
-                not os.path.isfile(os.path.join(full_path, '__init__.py'))):
+            if not namespace and not ispackage(full_path):
                 return None, False
 
             load_tests = None
diff -r f4c6dab59cd8 Lib/unittest/test/test_discovery.py
--- a/Lib/unittest/test/test_discovery.py	Tue Apr 26 17:04:18 2016 +0200
+++ b/Lib/unittest/test/test_discovery.py	Fri Apr 29 09:48:20 2016 +0200
@@ -409,23 +409,11 @@
         self.assertEqual(_find_tests_args, [(start_dir, 'pattern')])
         self.assertIn(top_level_dir, sys.path)
 
-    def test_discover_start_dir_is_package_calls_package_load_tests(self):
-        # This test verifies that the package load_tests in a package is indeed
-        # invoked when the start_dir is a package (and not the top level).
-        # http://bugs.python.org/issue22457
-
-        # Test data: we expect the following:
-        # an isfile to verify the package, then importing and scanning
-        # as per _find_tests' normal behaviour.
-        # We expect to see our load_tests hook called once.
-        vfs = {abspath('/toplevel'): ['startdir'],
-               abspath('/toplevel/startdir'): ['__init__.py']}
+    def _discover_start_dir_is_package_calls_package_load_tests(self, vfs):
         def list_dir(path):
-            return list(vfs[path])
+            return list(self.vfs[path])
         self.addCleanup(setattr, os, 'listdir', os.listdir)
         os.listdir = list_dir
-        self.addCleanup(setattr, os.path, 'isfile', os.path.isfile)
-        os.path.isfile = lambda path: path.endswith('.py')
         self.addCleanup(setattr, os.path, 'isdir', os.path.isdir)
         os.path.isdir = lambda path: not path.endswith('.py')
         self.addCleanup(sys.path.remove, abspath('/toplevel'))
@@ -454,6 +442,31 @@
         self.assertEqual(suite,
                          [['load_tests called startdir']])
 
+    def test_discover_start_dir_is_package_calls_package_load_tests(self):
+        # This test verifies that the package load_tests in a package is indeed
+        # invoked when the start_dir is a package (and not the top level).
+        # http://bugs.python.org/issue22457
+
+        # Test data: we expect the following:
+        # an isfile to verify the package, then importing and scanning
+        # as per _find_tests' normal behaviour.
+        # We expect to see our load_tests hook called once.
+        vfs = {abspath('/toplevel'): ['startdir'],
+               abspath('/toplevel/startdir'): ['__init__.py']}
+        self.addCleanup(setattr, os.path, 'isfile', os.path.isfile)
+        os.path.isfile = lambda path: path.endswith('.py')
+        self._discover_start_dir_is_package_calls_package_load_tests(vfs)
+
+    def test_discover_start_dir_is_package_with_byte_compiled__init__(self):
+        # This test verifies that the package load_tests in a package is
+        # invoked when the start_dir is a package with an __init__.pyc file.
+        # http://bugs.python.org/issue26859
+        vfs = {abspath('/toplevel'): ['startdir'],
+               abspath('/toplevel/startdir'): ['__init__.pyc']}
+        self.addCleanup(setattr, os.path, 'isfile', os.path.isfile)
+        os.path.isfile = lambda path: path.endswith('.pyc')
+        self._discover_start_dir_is_package_calls_package_load_tests(vfs)
+
     def setup_import_issue_tests(self, fakefile):
         listdir = os.listdir
         os.listdir = lambda _: [fakefile]