diff --git a/jedi/evaluate/docstrings.py b/jedi/evaluate/docstrings.py
index 9a51671a..e63745e5 100644
--- a/jedi/evaluate/docstrings.py
+++ b/jedi/evaluate/docstrings.py
@@ -191,7 +191,7 @@ def follow_param(module_context, param):
             [p for param_str in _search_param_in_docstr(docstring, str(param.name))
                 for p in _evaluate_for_statement_string(module_context, param_str)]
         )
-    func = param.parent_function
+    func = param.get_parent_function()
     types = eval_docstring(func.raw_doc)
     if func.name.value == '__init__':
         cls = search_ancestor(func, 'classdef')
diff --git a/jedi/evaluate/finder.py b/jedi/evaluate/finder.py
index 76687d7d..82e75948 100644
--- a/jedi/evaluate/finder.py
+++ b/jedi/evaluate/finder.py
@@ -98,7 +98,7 @@ class NameFinder(object):
         if self._context.predefined_names:
             # TODO is this ok? node might not always be a tree.Name
             node = self._name
-            while node is not None and not isinstance(node, tree.IsScope):
+            while node is not None and not node.is_scope():
                 node = node.parent
                 if node.type in ("if_stmt", "for_stmt", "comp_for"):
                     try:
diff --git a/jedi/parser/tree.py b/jedi/parser/tree.py
index ba2470e4..2a961a51 100644
--- a/jedi/parser/tree.py
+++ b/jedi/parser/tree.py
@@ -711,15 +711,6 @@ class ErrorLeaf(LeafWithNewLines):
             (type(self).__name__, self.original_type, repr(self.value), self.start_pos)
 
 
-class IsScopeMeta(type):
-    def __instancecheck__(self, other):
-        return other.is_scope()
-
-
-class IsScope(use_metaclass(IsScopeMeta)):
-    pass
-
-
 class Scope(BaseNode, DocstringMixin):
     """
     Super class for the parser tree, which represents the state of a python
@@ -1635,9 +1626,8 @@ class Param(BaseNode):
     def position_nr(self):
         return self.parent.children.index(self) - 1
 
-    @property
-    def parent_function(self):
-        return self.get_parent_until(IsScope)
+    def get_parent_function(self):
+        return search_ancestor(self, ('funcdef', 'lambda'))
 
     def __repr__(self):
         default = '' if self.default is None else '=%s' % self.default.get_code()