diff --git a/‎Lib/importlib/__init__.py‎
Lines changed: 11 additions & 4 deletions b/‎Lib/importlib/__init__.py‎
Lines changed: 11 additions & 4 deletions
diff --git a/‎Lib/test/test_importlib/test_api.py‎
Lines changed: 68 additions & 0 deletions b/‎Lib/test/test_importlib/test_api.py‎
Lines changed: 68 additions & 0 deletions
diff --git a/‎Misc/NEWS‎
Lines changed: 2 additions & 0 deletions b/‎Misc/NEWS‎
Lines changed: 2 additions & 0 deletions
@@ -153,10 +153,17 @@ def reload(module):
     _RELOADING[name] = module
     try:
         parent_name = name.rpartition('.')[0]
-        if parent_name and parent_name not in sys.modules:
-            msg = "parent {!r} not in sys.modules"
-            raise ImportError(msg.format(parent_name), name=parent_name)
-        spec = module.__spec__ = _bootstrap._find_spec(name, None, module)
+        if parent_name:
+            try:
+                parent = sys.modules[parent_name]
+            except KeyError:
+                msg = "parent {!r} not in sys.modules"
+                raise ImportError(msg.format(parent_name), name=parent_name)
+            else:
+                pkgpath = parent.__path__
+        else:
+            pkgpath = None
+        spec = module.__spec__ = _bootstrap._find_spec(name, pkgpath, module)
         methods = _bootstrap._SpecMethods(spec)
         methods.exec(module)
         # The module may have replaced itself in sys.modules!
 
@@ -4,13 +4,45 @@
 frozen_util, source_util = util.import_importlib('importlib.util')
 frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
 
+from contextlib import contextmanager
 import os.path
 import sys
 from test import support
 import types
 import unittest
 
 
+@contextmanager
+def temp_module(name, content='', *, pkg=False):
+    conflicts = [n for n in sys.modules if n.partition('.')[0] == name]
+    with support.temp_cwd(None) as cwd:
+        with util.uncache(name, *conflicts):
+            with support.DirsOnSysPath(cwd):
+                frozen_init.invalidate_caches()
+
+                location = os.path.join(cwd, name)
+                if pkg:
+                    modpath = os.path.join(location, '__init__.py')
+                    os.mkdir(name)
+                else:
+                    modpath = location + '.py'
+                    if content is None:
+                        # Make sure the module file gets created.
+                        content = ''
+                if content is not None:
+                    # not a namespace package
+                    with open(modpath, 'w') as modfile:
+                        modfile.write(content)
+                yield location
+
+
+def submodule(parent, name, pkg_dir, content=''):
+    path = os.path.join(pkg_dir, name + '.py')
+    with open(path, 'w') as subfile:
+        subfile.write(content)
+    return '{}.{}'.format(parent, name), path
+
+
 class ImportModuleTests:
 
     """Test importlib.import_module."""
@@ -246,6 +278,32 @@ def test_nothing(self):
         # None is returned upon failure to find a loader.
         self.assertIsNone(self.init.find_spec('nevergoingtofindthismodule'))
 
+    def test_find_submodule(self):
+        name = 'spam'
+        subname = 'ham'
+        with temp_module(name, pkg=True) as pkg_dir:
+            fullname, _ = submodule(name, subname, pkg_dir)
+            spec = self.init.find_spec(fullname, [pkg_dir])
+            self.assertIsNot(spec, None)
+            self.assertNotIn(name, sorted(sys.modules))
+            # Ensure successive calls behave the same.
+            spec_again = self.init.find_spec(fullname, [pkg_dir])
+            # XXX Once #19927 is resolved, uncomment this line.
+            #self.assertEqual(spec_again, spec)
+
+    def test_find_submodule_missing_path(self):
+        name = 'spam'
+        subname = 'ham'
+        with temp_module(name, pkg=True) as pkg_dir:
+            fullname, _ = submodule(name, subname, pkg_dir)
+            spec = self.init.find_spec(fullname)
+            self.assertIs(spec, None)
+            self.assertNotIn(name, sorted(sys.modules))
+            # Ensure successive calls behave the same.
+            spec = self.init.find_spec(fullname)
+            self.assertIs(spec, None)
+
+
 class Frozen_FindSpecTests(FindSpecTests, unittest.TestCase):
     init = frozen_init
     machinery = frozen_machinery
@@ -410,6 +468,16 @@ def test_reload_namespace_changed(self):
                     self.assertEqual(loader.path, init_path)
                     self.assertEqual(ns, expected)
 
+    def test_reload_submodule(self):
+        # See #19851.
+        name = 'spam'
+        subname = 'ham'
+        with temp_module(name, pkg=True) as pkg_dir:
+            fullname, _ = submodule(name, subname, pkg_dir)
+            ham = self.init.import_module(fullname)
+            reloaded = self.init.reload(ham)
+            self.assertIs(reloaded, ham)
+
 
 class Frozen_ReloadTests(ReloadTests, unittest.TestCase):
     init = frozen_init
 
@@ -114,6 +114,8 @@ Library
 - Issue #6477: Added support for pickling the types of built-in singletons
   (i.e., Ellipsis, NotImplemented, None).
 
+- Issue #19851: Fixed a regression in reloading sub-modules.
+
 - ssl.create_default_context() sets OP_NO_COMPRESSION to prevent CRIME.
 
 - Issue #19802: Add socket.SO_PRIORITY.