diff --git a/jedi/plugins/stdlib.py b/jedi/plugins/stdlib.py
index fba94894..5a9d55c5 100644
--- a/jedi/plugins/stdlib.py
+++ b/jedi/plugins/stdlib.py
@@ -789,6 +789,13 @@ def _os_path_join(args_set, callback):
     return callback()
 
 
+_path_overrides = {
+    'dirname': _create_string_input_function(os.path.dirname),
+    'abspath': _create_string_input_function(os.path.abspath),
+    'relpath': _create_string_input_function(os.path.relpath),
+    'join': _os_path_join,
+}
+
 _implemented = {
     'builtins': {
         'getattr': builtins_getattr,
@@ -851,12 +858,8 @@ _implemented = {
         # For now this works at least better than Jedi trying to understand it.
         'dataclass': _dataclass
     },
-    'os.path': {
-        'dirname': _create_string_input_function(os.path.dirname),
-        'abspath': _create_string_input_function(os.path.abspath),
-        'relpath': _create_string_input_function(os.path.relpath),
-        'join': _os_path_join,
-    }
+    'posixpath': _path_overrides,
+    'ntpath': _path_overrides,
 }
 
 
@@ -908,7 +911,8 @@ class EnumInstance(LazyValueWrapper):
 
 def tree_name_to_values(func):
     def wrapper(inference_state, context, tree_name):
-        if tree_name.value == 'sep' and context.is_module() and context.py__name__() == 'os.path':
+        if tree_name.value == 'sep' \
+                and context.is_module() and context.py__name__() in ('posixpath', 'ntpath'):
             return ValueSet({
                 compiled.create_simple_object(inference_state, os.path.sep),
             })
diff --git a/test/test_api/test_call_signatures.py b/test/test_api/test_call_signatures.py
index 90fbc0f8..3abd4761 100644
--- a/test/test_api/test_call_signatures.py
+++ b/test/test_api/test_call_signatures.py
@@ -210,9 +210,10 @@ def test_chained_calls(Script):
 def test_return(Script):
     source = dedent('''
     def foo():
-        return '.'.join()''')
+        return (1).conjugate()''')
 
-    assert_signature(Script, source, 'join', 0, column=len("    return '.'.join("))
+    assert_signature(
+        Script, source, 'conjugate', expected_index=None, column=len("    return (1).conjugate("))
 
 
 def test_find_signature_on_module(Script):
@@ -249,9 +250,9 @@ def test_complex(Script, environment):
     # Do these checks just for Python 3, I'm too lazy to deal with this
     # legacy stuff. ~ dave.
     assert get_signature(func1.tree_node) \
-        == 'compile(pattern: AnyStr, flags: _FlagsType = ...) -> Pattern[AnyStr]'
+        == 'compile(pattern: AnyStr, flags: _FlagsType = 0) -> Pattern[AnyStr]'
     assert get_signature(func2.tree_node) \
-        == 'compile(pattern: Pattern[AnyStr], flags: _FlagsType = ...) ->\nPattern[AnyStr]'
+        == 'compile(pattern: Pattern[AnyStr], flags: _FlagsType = 0) ->\nPattern[AnyStr]'
 
     # jedi-vim #70
     s = """def foo("""