diff --git a/jedi/evaluate/helpers.py b/jedi/evaluate/helpers.py
index c94a1fbe..497b81c6 100644
--- a/jedi/evaluate/helpers.py
+++ b/jedi/evaluate/helpers.py
@@ -172,7 +172,7 @@ def get_module_names(module, all_scopes):
         # parent_scope. There's None as a parent, because nodes in the module
         # node have the parent module and not suite as all the others.
         # Therefore it's important to catch that case.
-        names = [n for n in names if get_parent_scope(n).parent in (module, None)]
+        names = [n for n in names if get_parent_scope(n) == module]
     return names
 
 
diff --git a/jedi/evaluate/syntax_tree.py b/jedi/evaluate/syntax_tree.py
index 2b90a29a..5a2d5dc8 100644
--- a/jedi/evaluate/syntax_tree.py
+++ b/jedi/evaluate/syntax_tree.py
@@ -527,8 +527,6 @@ def tree_name_to_contexts(evaluator, context, tree_name):
             # which means the function itself.
             filters = [next(filters)]
             return finder.find(filters, attribute_lookup=False)
-        elif node.type == 'param':
-            raise NotImplementedError
         elif node.type not in ('import_from', 'import_name'):
             context = evaluator.create_context(context, tree_name)
             return eval_atom(context, tree_name)
@@ -571,6 +569,8 @@ def tree_name_to_contexts(evaluator, context, tree_name):
         # the static analysis report.
         exceptions = context.eval_node(tree_name.get_previous_sibling().get_previous_sibling())
         types = exceptions.execute_evaluated()
+    elif node.type == 'param':
+        types = NO_CONTEXTS
     else:
         raise ValueError("Should not happen. type: %s" % typ)
     return types
diff --git a/jedi/parser_utils.py b/jedi/parser_utils.py
index 212d70f2..2ee67f04 100644
--- a/jedi/parser_utils.py
+++ b/jedi/parser_utils.py
@@ -243,6 +243,9 @@ def get_parent_scope(node, include_flows=False):
     Returns the underlying scope.
     """
     scope = node.parent
+    if scope.type in ('funcdef', 'classdef') and scope.name == node:
+        scope = scope.parent
+
     while scope is not None:
         if include_flows and isinstance(scope, tree.Flow):
             return scope
diff --git a/test/test_api/test_defined_names.py b/test/test_api/test_defined_names.py
index ed5f1eb2..4df1181f 100644
--- a/test/test_api/test_defined_names.py
+++ b/test/test_api/test_defined_names.py
@@ -101,3 +101,20 @@ def test_names_twice(environment):
 def test_simple_name(environment):
     defs = names('foo', references=True, environment=environment)
     assert not defs[0]._name.infer()
+
+
+def test_no_error(environment):
+    code = dedent("""
+        def foo(a, b):
+            if a == 10:
+                if b is None:
+                    print("foo")
+                a = 20
+        """)
+    func_name, = names(code)
+    print(func_name.defined_names())
+    a, b, a20 = func_name.defined_names()
+    assert a.name == 'a'
+    assert b.name == 'b'
+    assert a20.name == 'a'
+    assert a20.goto_assignments() == [a20]