diff --git a/dill/_dill.py b/dill/_dill.py
index cddc9cf5..40831e66 100644
--- a/dill/_dill.py
+++ b/dill/_dill.py
@@ -397,50 +397,87 @@ def loads(str, ignore=None, **kwds):
 ### End: Shorthands ###
 
 ### Pickle the Interpreter Session
+SESSION_IMPORTED_AS_TYPES = (ModuleType, ClassType, TypeType, Exception,
+                             FunctionType, MethodType, BuiltinMethodType)
+
 def _module_map():
     """get map of imported modules"""
-    from collections import defaultdict
-    modmap = defaultdict(list)
+    from collections import defaultdict, namedtuple
+    modmap = namedtuple('Modmap', ['by_name', 'by_id', 'top_level'])
+    modmap = modmap(defaultdict(list), defaultdict(list), {})
     items = 'items' if PY3 else 'iteritems'
-    for name, module in getattr(sys.modules, items)():
-        if module is None:
+    for modname, module in getattr(sys.modules, items)():
+        if not isinstance(module, ModuleType):
             continue
-        for objname, obj in module.__dict__.items():
-            modmap[objname].append((obj, name))
+        if '.' not in modname:
+            modmap.top_level[id(module)] = modname
+        for objname, modobj in module.__dict__.items():
+            modmap.by_name[objname].append((modobj, modname))
+            modmap.by_id[id(modobj)].append((modobj, objname, modname))
     return modmap
 
-def _lookup_module(modmap, name, obj, main_module): #FIXME: needs work
-    """lookup name if module is imported"""
-    for modobj, modname in modmap[name]:
-        if modobj is obj and modname != main_module.__name__:
-            return modname
+def _lookup_module(modmap, name, obj, main_module):
+    """lookup name or id of obj if module is imported"""
+    for modobj, modname in modmap.by_name[name]:
+        if modobj is obj and sys.modules[modname] is not main_module:
+            return modname, name
+    if isinstance(obj, SESSION_IMPORTED_AS_TYPES):
+        for modobj, objname, modname in modmap.by_id[id(obj)]:
+            if sys.modules[modname] is not main_module:
+                return modname, objname
+    return None, None
 
 def _stash_modules(main_module):
     modmap = _module_map()
+    newmod = ModuleType(main_module.__name__)
+
     imported = []
+    imported_as = []
+    imported_top_level = []  # keep separeted for backwards compatibility
     original = {}
     items = 'items' if PY3 else 'iteritems'
     for name, obj in getattr(main_module.__dict__, items)():
-        source_module = _lookup_module(modmap, name, obj, main_module)
+        if obj is main_module:
+            original[name] = newmod  # self-reference
+            continue
+
+        # Avoid incorrectly matching a singleton value in another package (ex.: __doc__).
+        if any(obj is singleton for singleton in (None, False, True)) or \
+                isinstance(obj, ModuleType) and _is_builtin_module(obj):  # always saved by ref
+            original[name] = obj
+            continue
+
+        source_module, objname = _lookup_module(modmap, name, obj, main_module)
         if source_module:
-            imported.append((source_module, name))
+            if objname == name:
+                imported.append((source_module, name))
+            else:
+                imported_as.append((source_module, objname, name))
         else:
-            original[name] = obj
-    if len(imported):
-        import types
-        newmod = types.ModuleType(main_module.__name__)
+            try:
+                imported_top_level.append((modmap.top_level[id(obj)], name))
+            except KeyError:
+                original[name] = obj
+
+    if len(original) < len(main_module.__dict__):
         newmod.__dict__.update(original)
         newmod.__dill_imported = imported
+        newmod.__dill_imported_as = imported_as
+        newmod.__dill_imported_top_level = imported_top_level
         return newmod
     else:
-        return original
+        return main_module
 
-def _restore_modules(main_module):
-    if '__dill_imported' not in main_module.__dict__:
-        return
-    imports = main_module.__dict__.pop('__dill_imported')
-    for module, name in imports:
-        exec("from %s import %s" % (module, name), main_module.__dict__)
+def _restore_modules(unpickler, main_module):
+    try:
+        for modname, name in main_module.__dict__.pop('__dill_imported'):
+            main_module.__dict__[name] = unpickler.find_class(modname, name)
+        for modname, objname, name in main_module.__dict__.pop('__dill_imported_as'):
+            main_module.__dict__[name] = unpickler.find_class(modname, objname)
+        for modname, name in main_module.__dict__.pop('__dill_imported_top_level'):
+            main_module.__dict__[name] = __import__(modname)
+    except KeyError:
+        pass
 
 #NOTE: 06/03/15 renamed main_module to main
 def dump_session(filename='/tmp/session.pkl', main=None, byref=False, **kwds):
@@ -453,13 +490,16 @@ def dump_session(filename='/tmp/session.pkl', main=None, byref=False, **kwds):
     else:
         f = open(filename, 'wb')
     try:
+        pickler = Pickler(f, protocol, **kwds)
+        pickler._original_main = main
         if byref:
             main = _stash_modules(main)
-        pickler = Pickler(f, protocol, **kwds)
         pickler._main = main     #FIXME: dill.settings are disabled
         pickler._byref = False   # disable pickling by name reference
         pickler._recurse = False # disable pickling recursion for globals
         pickler._session = True  # is best indicator of when pickling a session
+        pickler._first_pass = True
+        pickler._main_modified = main is not pickler._original_main
         pickler.dump(main)
     finally:
         if f is not filename:  # If newly opened file
@@ -480,7 +520,7 @@ def load_session(filename='/tmp/session.pkl', main=None, **kwds):
         module = unpickler.load()
         unpickler._session = False
         main.__dict__.update(module.__dict__)
-        _restore_modules(main)
+        _restore_modules(unpickler, main)
     finally:
         if f is not filename:  # If newly opened file
             f.close()
@@ -1060,9 +1100,11 @@ def _import_module(import_name, safe=False):
             return None
         raise
 
-def _locate_function(obj, session=False):
-    if obj.__module__ in ['__main__', None]: # and session:
+def _locate_function(obj, pickler=None):
+    if obj.__module__ in ['__main__', None] or \
+            pickler and pickler._session and obj.__module__ == pickler._main.__name__:
         return False
+
     found = _import_module(obj.__module__ + '.' + obj.__name__, safe=True)
     return found is obj
 
@@ -1177,7 +1219,8 @@ def save_code(pickler, obj):
 
 @register(dict)
 def save_module_dict(pickler, obj):
-    if is_dill(pickler, child=False) and obj == pickler._main.__dict__ and not pickler._session:
+    if is_dill(pickler, child=False) and obj == pickler._main.__dict__ and \
+            not (pickler._session and pickler._first_pass):
         log.info("D1: <dict%s" % str(obj.__repr__).split('dict')[-1]) # obj
         if PY3:
             pickler.write(bytes('c__builtin__\n__main__\n', 'UTF-8'))
@@ -1204,7 +1247,7 @@ def save_module_dict(pickler, obj):
         log.info("D2: <dict%s" % str(obj.__repr__).split('dict')[-1]) # obj
         if is_dill(pickler, child=False) and pickler._session:
             # we only care about session the first pass thru
-            pickler._session = False
+            pickler._first_pass = False
         StockPickler.save_dict(pickler, obj)
         log.info("# D2")
     return
@@ -1267,7 +1310,7 @@ def save_dict_items(pickler, obj):
 
 @register(ClassType)
 def save_classobj(pickler, obj): #FIXME: enable pickler._byref
-    if obj.__module__ == '__main__': #XXX: use _main_module.__name__ everywhere?
+    if not _locate_function(obj, pickler):
         log.info("C1: %s" % obj)
         pickler.save_reduce(ClassType, (obj.__name__, obj.__bases__,
                                         obj.__dict__), obj=obj)
@@ -1676,6 +1719,16 @@ def save_weakproxy(pickler, obj):
     log.info("# %s" % _t)
     return
 
+def _is_builtin_module(module):
+    if not hasattr(module, "__file__"): return True
+    # If a module file name starts with prefix, it should be a builtin
+    # module, so should always be pickled as a reference.
+    names = ["base_prefix", "base_exec_prefix", "exec_prefix", "prefix", "real_prefix"]
+    return any(os.path.realpath(module.__file__).startswith(os.path.realpath(getattr(sys, name)))
+               for name in names if hasattr(sys, name)) or \
+            module.__file__.endswith(EXTENSION_SUFFIXES) or \
+            'site-packages' in module.__file__
+
 @register(ModuleType)
 def save_module(pickler, obj):
     if False: #_use_diff:
@@ -1696,19 +1749,9 @@ def save_module(pickler, obj):
         pickler.save_reduce(_import_module, (obj.__name__,), obj=obj)
         log.info("# M1")
     else:
-        # if a module file name starts with prefix, it should be a builtin
-        # module, so should be pickled as a reference
-        if hasattr(obj, "__file__"):
-            names = ["base_prefix", "base_exec_prefix", "exec_prefix",
-                     "prefix", "real_prefix"]
-            builtin_mod = any(os.path.realpath(obj.__file__).startswith(os.path.realpath(getattr(sys, name)))
-                              for name in names if hasattr(sys, name))
-            builtin_mod = (builtin_mod or obj.__file__.endswith(EXTENSION_SUFFIXES) or
-                           'site-packages' in obj.__file__)
-        else:
-            builtin_mod = True
-        if obj.__name__ not in ("builtins", "dill", "dill._dill") \
-           and not builtin_mod or is_dill(pickler, child=True) and obj is pickler._main:
+        builtin_mod = _is_builtin_module(obj)
+        if obj.__name__ not in ("builtins", "dill", "dill._dill") and not builtin_mod or \
+                is_dill(pickler, child=True) and obj is pickler._main:
             log.info("M1: %s" % obj)
             _main_dict = obj.__dict__.copy() #XXX: better no copy? option to copy?
             [_main_dict.pop(item, None) for item in singletontypes
@@ -1766,7 +1809,7 @@ def save_type(pickler, obj, postproc_list=None):
         obj_name = getattr(obj, '__qualname__', getattr(obj, '__name__', None))
         _byref = getattr(pickler, '_byref', None)
         obj_recursive = id(obj) in getattr(pickler, '_postproc', ())
-        incorrectly_named = not _locate_function(obj)
+        incorrectly_named = not _locate_function(obj, pickler)
         if not _byref and not obj_recursive and incorrectly_named: # not a function, but the name was held over
             if issubclass(type(obj), type):
                 # thanks to Tom Stepleton pointing out pickler._session unneeded
@@ -1844,11 +1887,12 @@ def save_classmethod(pickler, obj):
 
 @register(FunctionType)
 def save_function(pickler, obj):
-    if not _locate_function(obj): #, pickler._session):
+    if not _locate_function(obj, pickler):
         log.info("F1: %s" % obj)
         _recurse = getattr(pickler, '_recurse', None)
         _byref = getattr(pickler, '_byref', None)
         _postproc = getattr(pickler, '_postproc', None)
+        _main_modified = getattr(pickler, '_main_modified', None)
         postproc_list = []
         if _recurse:
             # recurse to get all globals referred to by obj
@@ -1863,8 +1907,12 @@ def save_function(pickler, obj):
         else:
             globs_copy = obj.__globals__ if PY3 else obj.func_globals
 
+            # If the globals is the __dict__ from the module being save as a
+            # session, substitute it by the dictionary being actually saved.
+            if _main_modified and globs_copy is pickler._original_main.__dict__:
+                globs = globs_copy = pickler._main.__dict__
             # If the globals is a module __dict__, do not save it in the pickle.
-            if globs_copy is not None and obj.__module__ is not None and \
+            elif globs_copy is not None and obj.__module__ is not None and \
                     getattr(_import_module(obj.__module__, True), '__dict__', None) is globs_copy:
                 globs = globs_copy
             else:
diff --git a/tests/__main__.py b/tests/__main__.py
index c64168d1..e82993c6 100644
--- a/tests/__main__.py
+++ b/tests/__main__.py
@@ -28,4 +28,3 @@
         if not p:
             print('.', end='')
     print('')
-
diff --git a/tests/test_session.py b/tests/test_session.py
new file mode 100644
index 00000000..fd71ea05
--- /dev/null
+++ b/tests/test_session.py
@@ -0,0 +1,243 @@
+#!/usr/bin/env python
+
+# Author: Leonardo Gama (@leogama)
+# Copyright (c) 2022 The Uncertainty Quantification Foundation.
+# License: 3-clause BSD.  The full license text is available at:
+#  - https://github.com/uqfoundation/dill/blob/master/LICENSE
+
+from __future__ import print_function
+import atexit, dill, os, sys, __main__
+
+session_file = os.path.join(os.path.dirname(__file__), 'session-byref-%s.pkl')
+
+def test_modules(main, byref):
+    main_dict = main.__dict__
+
+    try:
+        for obj in ('json', 'url', 'local_mod', 'sax', 'dom'):
+            assert main_dict[obj].__name__ in sys.modules
+
+        for obj in ('Calendar', 'isleap'):
+            assert main_dict[obj] is sys.modules['calendar'].__dict__[obj]
+        assert main.day_name.__module__ == 'calendar'
+        if byref:
+            assert main.day_name is sys.modules['calendar'].__dict__['day_name']
+
+        assert main.complex_log is sys.modules['cmath'].__dict__['log']
+
+    except AssertionError:
+        import traceback
+        error_line = traceback.format_exc().splitlines()[-2].replace('[obj]', '['+repr(obj)+']')
+        print("Error while testing (byref=%s):" % byref, error_line, sep="\n", file=sys.stderr)
+        raise
+
+
+# Test session loading in a fresh interpreter session.
+if __name__ == '__main__' and len(sys.argv) >= 3 and sys.argv[1] == '--child':
+    byref = sys.argv[2] == 'True'
+    dill.load_session(session_file % byref)
+    test_modules(__main__, byref)
+    sys.exit()
+
+del test_modules
+
+
+def _clean_up_cache(module):
+    cached = module.__file__.split('.', 1)[0] + '.pyc'
+    cached = module.__cached__ if hasattr(module, '__cached__') else cached
+    pycache = os.path.join(os.path.dirname(module.__file__), '__pycache__')
+    for remove, file in [(os.remove, cached), (os.removedirs, pycache)]:
+        try:
+            remove(file)
+        except OSError:
+            pass
+
+
+# To clean up namespace before loading the session.
+original_modules = set(sys.modules.keys()) - \
+        set(['json', 'urllib', 'xml.sax', 'xml.dom.minidom', 'calendar', 'cmath'])
+original_objects = set(__main__.__dict__.keys())
+original_objects.add('original_objects')
+
+
+# Create various kinds of objects to test different internal logics.
+
+## Modules.
+import json                                         # top-level module
+import urllib as url                                # top-level module under alias
+from xml import sax                                 # submodule
+import xml.dom.minidom as dom                       # submodule under alias
+import test_dictviews as local_mod                  # non-builtin top-level module
+atexit.register(_clean_up_cache, local_mod)
+
+## Imported objects.
+from calendar import Calendar, isleap, day_name     # class, function, other object
+from cmath import log as complex_log                # imported with alias
+
+## Local objects.
+x = 17
+empty = None
+names = ['Alice', 'Bob', 'Carol']
+def squared(x): return x**2
+cubed = lambda x: x**3
+class Person:
+    def __init__(self, name, age):
+        self.name = name
+        self.age = age
+person = Person(names[0], x)
+class CalendarSubclass(Calendar):
+    def weekdays(self):
+        return [day_name[i] for i in self.iterweekdays()]
+cal = CalendarSubclass()
+selfref = __main__
+
+
+def test_objects(main, copy_dict, byref):
+    main_dict = main.__dict__
+
+    try:
+        for obj in ('json', 'url', 'local_mod', 'sax', 'dom'):
+            assert main_dict[obj].__name__ == copy_dict[obj].__name__
+
+        #FIXME: In the second test call, 'calendar' is not included in
+        # sys.modules, independent of the value of byref. Tried to run garbage
+        # collection before with no luck. This block fails even with
+        # "import calendar" before it. Needed to restore the original modules
+        # with the 'copy_modules' object. (Moved to "test_session_{1,2}.py".)
+
+        #for obj in ('Calendar', 'isleap'):
+        #    assert main_dict[obj] is sys.modules['calendar'].__dict__[obj]
+        #assert main_dict['day_name'].__module__ == 'calendar'
+        #if byref:
+        #    assert main_dict['day_name'] is sys.modules['calendar'].__dict__['day_name']
+
+        for obj in ('x', 'empty', 'names'):
+            assert main_dict[obj] == copy_dict[obj]
+
+        globs = '__globals__' if dill._dill.PY3 else 'func_globals'
+        for obj in ['squared', 'cubed']:
+            assert getattr(main_dict[obj], globs) is main_dict
+            assert main_dict[obj](3) == copy_dict[obj](3)
+
+        assert main.Person.__module__ == main.__name__
+        assert isinstance(main.person, main.Person)
+        assert main.person.age == copy_dict['person'].age
+
+        assert issubclass(main.CalendarSubclass, main.Calendar)
+        assert isinstance(main.cal, main.CalendarSubclass)
+        assert main.cal.weekdays() == copy_dict['cal'].weekdays()
+
+        assert main.selfref is main
+
+    except AssertionError:
+        import traceback
+        error_line = traceback.format_exc().splitlines()[-2].replace('[obj]', '['+repr(obj)+']')
+        print("Error while testing (byref=%s):" % byref, error_line, sep="\n", file=sys.stderr)
+        raise
+
+
+if __name__ == '__main__':
+
+    # Test dump_session() and load_session().
+    for byref in (False, True):
+        if byref:
+            # Test unpickleable imported object in main.
+            from sys import flags
+
+        #print(sorted(set(sys.modules.keys()) - original_modules))
+        dill._test_file = dill._dill.StringIO()
+        try:
+            # For the subprocess.
+            dill.dump_session(session_file % byref, byref=byref)
+
+            dill.dump_session(dill._test_file, byref=byref)
+            dump = dill._test_file.getvalue()
+            dill._test_file.close()
+
+            import __main__
+            copy_dict = __main__.__dict__.copy()
+            copy_modules = sys.modules.copy()
+            del copy_dict['dump']
+            del copy_dict['__main__']
+            for name in copy_dict.keys():
+                if name not in original_objects:
+                    del __main__.__dict__[name]
+            for module in list(sys.modules.keys()):
+                if module not in original_modules:
+                    del sys.modules[module]
+
+            dill._test_file = dill._dill.StringIO(dump)
+            dill.load_session(dill._test_file)
+            #print(sorted(set(sys.modules.keys()) - original_modules))
+
+            # Test session loading in a new session.
+            from dill.tests.__main__ import python, shell, sp
+            error = sp.call([python, __file__, '--child', str(byref)], shell=shell)
+            if error: sys.exit(error)
+            del python, shell, sp
+
+        finally:
+            dill._test_file.close()
+            try:
+                os.remove(session_file % byref)
+            except OSError:
+                pass
+
+        test_objects(__main__, copy_dict, byref)
+        __main__.__dict__.update(copy_dict)
+        sys.modules.update(copy_modules)
+        del __main__, copy_dict, copy_modules, dump
+
+
+    # This is for code coverage, tests the use case of dump_session(byref=True)
+    # without imported objects in the namespace. It's a contrived example because
+    # even dill can't be in it.
+    from types import ModuleType
+    modname = '__test_main__'
+    main = ModuleType(modname)
+    main.x = 42
+
+    _main = dill._dill._stash_modules(main)
+    if _main is not main:
+        print("There are objects to save by referenece that shouldn't be:",
+              _main.__dill_imported, _main.__dill_imported_as, _main.__dill_imported_top_level,
+              file=sys.stderr)
+
+    test_file = dill._dill.StringIO()
+    try:
+        dill.dump_session(test_file, main=main, byref=True)
+        dump = test_file.getvalue()
+        test_file.close()
+
+        sys.modules[modname] = ModuleType(modname)  # empty
+        # This should work after fixing https://github.com/uqfoundation/dill/issues/462
+        test_file = dill._dill.StringIO(dump)
+        dill.load_session(test_file)
+    finally:
+        test_file.close()
+
+    assert x == 42
+
+
+    # Dump session for module that is not __main__:
+    import test_classdef as module
+    atexit.register(_clean_up_cache, module)
+    module.selfref = module
+    dict_objects = [obj for obj in module.__dict__.keys() if not obj.startswith('__')]
+
+    test_file = dill._dill.StringIO()
+    try:
+        dill.dump_session(test_file, main=module)
+        dump = test_file.getvalue()
+        test_file.close()
+
+        for obj in dict_objects:
+            del module.__dict__[obj]
+
+        test_file = dill._dill.StringIO(dump)
+        dill.load_session(test_file, main=module)
+    finally:
+        test_file.close()
+
+    assert all(obj in module.__dict__ for obj in dict_objects)
+    assert module.selfref is module