diff --git a/Lib/unittest/loader.py b/Lib/unittest/loader.py
index c776f16c306..b254c8086b6 100644
--- a/Lib/unittest/loader.py
+++ b/Lib/unittest/loader.py
@@ -479,6 +479,8 @@ class TestLoader(object):
                     return tests, True
                 finally:
                     self._loading_packages.discard(name)
+        else:
+            return None, False
 
 
 defaultTestLoader = TestLoader()
diff --git a/Lib/unittest/test/test_discovery.py b/Lib/unittest/test/test_discovery.py
index 55921febf58..bb196e6997a 100644
--- a/Lib/unittest/test/test_discovery.py
+++ b/Lib/unittest/test/test_discovery.py
@@ -90,6 +90,46 @@ class TestDiscovery(unittest.TestCase):
                     ('test3', 'test4')])
         self.assertEqual(suite, expected)
 
+    def test_find_tests_socket(self):
+        # A socket is neither a directory nor a regular file.
+        # https://bugs.python.org/issue25320
+        loader = unittest.TestLoader()
+
+        original_listdir = os.listdir
+        def restore_listdir():
+            os.listdir = original_listdir
+        original_isfile = os.path.isfile
+        def restore_isfile():
+            os.path.isfile = original_isfile
+        original_isdir = os.path.isdir
+        def restore_isdir():
+            os.path.isdir = original_isdir
+
+        path_lists = [['socket']]
+        os.listdir = lambda path: path_lists.pop(0)
+        self.addCleanup(restore_listdir)
+
+        os.path.isdir = lambda path: False
+        self.addCleanup(restore_isdir)
+
+        os.path.isfile = lambda path: False
+        self.addCleanup(restore_isfile)
+
+        loader._get_module_from_name = lambda path: path + ' module'
+        orig_load_tests = loader.loadTestsFromModule
+        def loadTestsFromModule(module, pattern=None):
+            # This is where load_tests is called.
+            base = orig_load_tests(module, pattern=pattern)
+            return base + [module + ' tests']
+        loader.loadTestsFromModule = loadTestsFromModule
+        loader.suiteClass = lambda thing: thing
+
+        top_level = os.path.abspath('/foo')
+        loader._top_level_dir = top_level
+        suite = list(loader._find_tests(top_level, 'test*.py'))
+
+        self.assertEqual(suite, [])
+
     def test_find_tests_with_package(self):
         loader = unittest.TestLoader()
 
diff --git a/Misc/ACKS b/Misc/ACKS
index 5f1f300b110..10ac51e8add 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -396,6 +396,7 @@ Lance Ellinghaus
 Daniel Ellis
 Phil Elson
 David Ely
+Victor van den Elzen
 Jeff Epler
 Tom Epperly
 Gökcen Eraslan
diff --git a/Misc/NEWS b/Misc/NEWS
index 5233a43eb29..24dd75cadd3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -218,6 +218,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #25320: Handle sockets in directories unittest discovery is scanning.
+  Patch from Victor van den Elzen.
+
 - Issue #16181: cookiejar.http2time() now returns None if year is higher than
   datetime.MAXYEAR.