diff --git a/jedi/api/__init__.py b/jedi/api/__init__.py
index 24087a42..257f8c8d 100644
--- a/jedi/api/__init__.py
+++ b/jedi/api/__init__.py
@@ -304,7 +304,10 @@ class Script(object):
         if call_signature_details is None:
             return []
 
-        context = self._evaluator.create_context(call_signature_details.bracket_leaf)
+        context = self._evaluator.create_context(
+            self._get_module(),
+            call_signature_details.bracket_leaf
+        )
         with common.scale_speed_settings(settings.scale_call_signatures):
             definitions = helpers.cache_call_signatures(
                 self._evaluator,
diff --git a/jedi/api/completion.py b/jedi/api/completion.py
index 9eb91604..b1f487cd 100644
--- a/jedi/api/completion.py
+++ b/jedi/api/completion.py
@@ -15,7 +15,7 @@ def get_call_signature_param_names(call_signatures):
     # add named params
     for call_sig in call_signatures:
         # Allow protected access, because it's a public API.
-        module = call_sig._name.get_parent_until()
+        module = call_sig._name.get_root_context()
         # Compiled modules typically don't allow keyword arguments.
         if not isinstance(module, compiled.CompiledObject):
             for p in call_sig.params:
diff --git a/jedi/evaluate/context.py b/jedi/evaluate/context.py
index 7b60c119..9e2a4412 100644
--- a/jedi/evaluate/context.py
+++ b/jedi/evaluate/context.py
@@ -99,9 +99,17 @@ class LazyTreeContext(AbstractLazyContext):
     def __init__(self, context, node):
         super(LazyTreeContext, self).__init__(node)
         self._context = context
+        # We need to save the predefined names. It's an unfortunate side effect
+        # that needs to be tracked otherwise results will be wrong.
+        self._predefined_names = dict(context.predefined_names)
 
     def infer(self):
-        return self._context.eval_node(self.data)
+        old, self._context.predefined_names = \
+            self._context.predefined_names, self._predefined_names
+        try:
+            return self._context.eval_node(self.data)
+        finally:
+            self._context.predefined_names = old
 
 
 def get_merged_lazy_context(lazy_contexts):