diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 5cfda88..3230abe 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -23,6 +23,7 @@ Fixed
 - Don't ignore ``KeyError`` in call to instantiate_classes #81.
 - Optional subcommands fail with a KeyError #68.
 - Conflicting namespace for subclass key in subcommand.
+- ``instantiate_classes`` not working for subcommand keys #70.
 
 Changed
 ^^^^^^^
diff --git a/jsonargparse/actions.py b/jsonargparse/actions.py
index ac3b78a..6cedc61 100644
--- a/jsonargparse/actions.py
+++ b/jsonargparse/actions.py
@@ -733,14 +733,10 @@ class _ActionSubCommands(_SubParsersAction):
 
 
     @staticmethod
-    def handle_subcommands(parser, cfg, env, defaults, prefix='', fail_no_subcommand=True):
-        """Adds sub-command dest if missing and parses defaults and environment variables."""
+    def get_subcommand(parser, cfg_dict:dict, prefix:str='', fail_no_subcommand:bool=True):
+        """Returns the sub-command name and corresponding subparser."""
         if parser._subparsers is None:
-            return
-
-        cfg_dict = cfg.__dict__ if isinstance(cfg, Namespace) else cfg
-        cfg_keys = set(vars(_dict_to_flat_namespace(cfg)).keys())
-        cfg_keys = cfg_keys.union(set(cfg_dict.keys()))
+            return None, None
 
         # Get subcommands action
         for action in parser._actions:
@@ -760,11 +756,27 @@ class _ActionSubCommands(_SubParsersAction):
             cfg_dict[dest] = subcommand
 
         if subcommand is None and not (fail_no_subcommand and action._required):
-            return
+            return None, None
         if action._required and subcommand not in action._name_parser_map:
             raise KeyError('Sub-command "'+dest+'" is required but not given or its value is None.')
 
-        subparser = action._name_parser_map[subcommand]
+        subparser = action._name_parser_map.get(subcommand)
+
+        return subcommand, subparser
+
+
+    @staticmethod
+    def handle_subcommands(parser, cfg, env, defaults, prefix='', fail_no_subcommand=True):
+        """Adds sub-command dest if missing and parses defaults and environment variables."""
+
+        cfg_dict = cfg.__dict__ if isinstance(cfg, Namespace) else cfg
+
+        subcommand, subparser = _ActionSubCommands.get_subcommand(parser, cfg_dict, prefix=prefix, fail_no_subcommand=fail_no_subcommand)
+        if subcommand is None:
+            return
+
+        cfg_keys = set(vars(_dict_to_flat_namespace(cfg)).keys())
+        cfg_keys = cfg_keys.union(set(cfg_dict.keys()))
 
         # merge environment variable values and default values
         subnamespace = None
diff --git a/jsonargparse/core.py b/jsonargparse/core.py
index 89d3790..b78ca77 100644
--- a/jsonargparse/core.py
+++ b/jsonargparse/core.py
@@ -1117,6 +1117,11 @@ class ArgumentParser(_ActionsContainer, argparse.ArgumentParser, LoggerProperty)
                 component.instantiate_class(component, cfg)
                 _ActionLink.apply_instantiation_links(self, cfg, component.dest)
 
+        cfg_dict = cfg.__dict__ if isinstance(cfg, Namespace) else cfg
+        subcommand, subparser = _ActionSubCommands.get_subcommand(self, cfg_dict, fail_no_subcommand=False)
+        if subcommand:
+            cfg[subcommand] = subparser.instantiate_classes(cfg[subcommand], instantiate_groups=instantiate_groups)
+
         return cfg
 
 

diff --git a/jsonargparse_tests/signatures_tests.py b/jsonargparse_tests/signatures_tests.py
index e0506e9..966b7da 100755
--- a/jsonargparse_tests/signatures_tests.py
+++ b/jsonargparse_tests/signatures_tests.py
@@ -644,6 +644,24 @@ class SignaturesTests(unittest.TestCase):
         self.assertIsInstance(cfg['e'], EmptyInitClass)
 
 
+    def test_instantiate_classes_subcommand(self):
+        class Foo:
+            def __init__(self, a: int = 1):
+                self.a = a
+
+        parser = ArgumentParser(parse_as_dict=True)
+        subcommands = parser.add_subcommands()
+        subparser = ArgumentParser()
+        key = "foo"
+        subparser.add_class_arguments(Foo, key)
+        subcommand = "cmd"
+        subcommands.add_subcommand(subcommand, subparser)
+
+        config = parser.parse_args([subcommand])
+        config_init = parser.instantiate_classes(config)
+        self.assertIsInstance(config_init[subcommand][key], Foo)
+
+
     def test_implicit_optional(self):
 
         def func(a1: int = None):

Support for subcommands and `instantiate_classes`
I'm trying to use subcommands and `instantiate_classes` together.

Without subcommand, everything works properly:

```python
from jsonargparse import ArgumentParser

class Foo:
    def __init__(self, a: int = 1):
        ...

parser = ArgumentParser(parse_as_dict=True)
key = "foo"
parser.add_class_arguments(Foo, key)

config = parser.parse_args()
print(config)
config_init = parser.instantiate_classes(config)
# the class should be instantiated
print(config_init)
assert isinstance(config_init[key], Foo)
```

```python
{'foo': {'a': 1}}
{'foo': <__main__.Foo object at 0x102fc90d0>}
```

However, with subcommand enabled, seems like `instantiate_classes` does not act recursively.

```python
from jsonargparse import ArgumentParser

class Foo:
    def __init__(self, a: int = 1):
        ...

parser = ArgumentParser(parse_as_dict=True)
subcommands = parser.add_subcommands()
subparser = ArgumentParser()
key = "foo"
subparser.add_class_arguments(Foo, key)
subcommand = "cmd"
subcommands.add_subcommand(subcommand, subparser)

config = parser.parse_args([subcommand])
print(config)
# the class should be instantiated even if it is under a subcommand
config_init = parser.instantiate_classes(config)
print(config_init)
assert isinstance(config_init[subcommand][key], Foo)
```

```python
{'subcommand': 'cmd', 'cmd': {'foo': {'a': 1}}}
{'subcommand': 'cmd', 'cmd': {'foo': {'a': 1}}}
Traceback (most recent call last):
  File "script.py", line 33, in <module>
    assert isinstance(config_init[subcommand][key], Foo)
AssertionError
```

I would expect the second print to be

```python
{'subcommand': 'cmd', 'cmd': {'foo': <__main__.Foo object at 0x102fc90d0>}}
```

Not sure if this is a bug or a feature. Is this not a valid way to instantiate classes under subcommands?

If I try to do instead

```python
config_init = parser.instantiate_classes(config["subcommand"])
print(config_init)
```

I get:

```python
Traceback (most recent call last):
  File "/Users/carlosmocholi/Library/Application Support/JetBrains/PyCharmCE2020.3/scratches/scratch_12.py", line 32, in <module>
    config_init = parser.instantiate_classes(config["subcommand"])
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/core.py", line 1103, in instantiate_classes
    cfg = strip_meta(cfg)
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/util.py", line 247, in strip_meta
    cfg = namespace_to_dict(cfg)
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/util.py", line 233, in namespace_to_dict
    return expand_namespace(cfg_ns)
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/util.py", line 224, in expand_namespace
    cfg = dict(vars(cfg))
TypeError: vars() argument must have __dict__ attribute
```
jsonargparse_tests/signatures_tests.py::SignaturesTests::test_instantiate_classes_subcommand
jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_class_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_class_from_function_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_class_implemented_with_new jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_function_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_method_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_subclass_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_subclass_arguments_tuple jsonargparse_tests/signatures_tests.py::SignaturesTests::test_add_subclass_discard_init_args jsonargparse_tests/signatures_tests.py::SignaturesTests::test_basic_subtypes jsonargparse_tests/signatures_tests.py::SignaturesTests::test_fail_untyped_false jsonargparse_tests/signatures_tests.py::SignaturesTests::test_final_class jsonargparse_tests/signatures_tests.py::SignaturesTests::test_implicit_optional jsonargparse_tests/signatures_tests.py::SignaturesTests::test_instantiate_classes jsonargparse_tests/signatures_tests.py::SignaturesTests::test_invalid_type jsonargparse_tests/signatures_tests.py::SignaturesTests::test_link_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_link_arguments_apply_on_instantiate jsonargparse_tests/signatures_tests.py::SignaturesTests::test_link_arguments_subclasses jsonargparse_tests/signatures_tests.py::SignaturesTests::test_logger_debug jsonargparse_tests/signatures_tests.py::SignaturesTests::test_optional_enum jsonargparse_tests/signatures_tests.py::SignaturesTests::test_print_config jsonargparse_tests/signatures_tests.py::SignaturesTests::test_required_group jsonargparse_tests/signatures_tests.py::SignaturesTests::test_skip jsonargparse_tests/signatures_tests.py::SignaturesTests::test_skip_in_add_subclass_arguments jsonargparse_tests/signatures_tests.py::SignaturesTests::test_skip_within_subclass_type jsonargparse_tests/signatures_tests.py::SignaturesTests::test_type_any_serialize jsonargparse_tests/signatures_tests.py::SignaturesConfigTests::test_add_function_arguments_config jsonargparse_tests/signatures_tests.py::SignaturesConfigTests::test_add_subclass_arguments_with_config jsonargparse_tests/signatures_tests.py::SignaturesConfigTests::test_config_within_config