diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 6d2c4f5..1c7eb9e 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -433,7 +433,10 @@
 
 
 __all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
-           "getoutput", "check_output", "CalledProcessError", "DEVNULL"]
+           "getoutput", "check_output", "CalledProcessError", "DEVNULL",
+           "SubprocessError", "TimeoutExpired"]
+           # NOTE: We intentionally exclude list2cmdline as it is
+           # considered an internal implementation detail.  issue10838.
 
 if mswindows:
     from _winapi import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index e25cccd..71481bc 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -2420,6 +2420,21 @@
         subprocess._PopenSelector = self.orig_selector
         ProcessTestCase.tearDown(self)
 
+    def test__all__(self):
+        """Ensure that __all__ is populated properly."""
+        intentionally_excluded = set(("list2cmdline", "mswindows", "MAXFD"))
+        exported = set(subprocess.__all__)
+        possible_exports = set()
+        import types
+        for name, value in subprocess.__dict__.items():
+            if name.startswith('_'):
+                continue
+            if isinstance(value, (types.ModuleType,)):
+                continue
+            possible_exports.add(name)
+        self.assertEqual(exported, possible_exports - intentionally_excluded)
+
+
 
 @unittest.skipUnless(mswindows, "Windows-specific tests")
 class CommandsWithSpaces (BaseTestCase):