diff --git a/jedi/api/classes.py b/jedi/api/classes.py
index fba9b5ad..ee741c33 100644
--- a/jedi/api/classes.py
+++ b/jedi/api/classes.py
@@ -27,7 +27,7 @@ from jedi.inference.compiled.mixed import MixedName
 from jedi.inference.names import ImportName, SubModuleName
 from jedi.inference.gradual.stub_value import StubModuleValue
 from jedi.inference.gradual.conversion import convert_names, convert_values
-from jedi.inference.base_value import ValueSet
+from jedi.inference.base_value import ValueSet, HasNoContext
 from jedi.api.keywords import KeywordName
 from jedi.api import completion_cache
 from jedi.api.helpers import filter_follow_imports
@@ -37,13 +37,17 @@ def _sort_names_by_start_pos(names):
     return sorted(names, key=lambda s: s.start_pos or (0, 0))
 
 
-def defined_names(inference_state, context):
+def defined_names(inference_state, value):
     """
     List sub-definitions (e.g., methods in class).
 
     :type scope: Scope
     :rtype: list of Name
     """
+    try:
+        context = value.as_context()
+    except HasNoContext:
+        return []
     filter = next(context.get_filters())
     names = [name for name in filter.values()]
     return [Name(inference_state, n) for n in _sort_names_by_start_pos(names)]
@@ -759,7 +763,7 @@ class Name(BaseName):
         """
         defs = self._name.infer()
         return sorted(
-            unite(defined_names(self._inference_state, d.as_context()) for d in defs),
+            unite(defined_names(self._inference_state, d) for d in defs),
             key=lambda s: s._name.start_pos or (0, 0)
         )
 
diff --git a/jedi/inference/base_value.py b/jedi/inference/base_value.py
index e51e063c..31b72937 100644
--- a/jedi/inference/base_value.py
+++ b/jedi/inference/base_value.py
@@ -22,6 +22,10 @@ from jedi.cache import memoize_method
 sentinel = object()
 
 
+class HasNoContext(Exception):
+    pass
+
+
 class HelperValueMixin:
     def get_root_context(self):
         value = self
@@ -261,7 +265,7 @@ class Value(HelperValueMixin):
         return self.parent_context.is_stub()
 
     def _as_context(self):
-        raise NotImplementedError('Not all values need to be converted to contexts: %s', self)
+        raise HasNoContext
 
     @property
     def name(self):
diff --git a/test/test_api/test_names.py b/test/test_api/test_names.py
index d43a29bb..287a301e 100644
--- a/test/test_api/test_names.py
+++ b/test/test_api/test_names.py
@@ -189,3 +189,9 @@ def test_no_error(get_names):
 def test_is_side_effect(get_names, code, index, is_side_effect):
     names = get_names(code, references=True, all_scopes=True)
     assert names[index].is_side_effect() == is_side_effect
+
+
+def test_no_defined_names(get_names):
+    definition, = get_names("x = (1, 2)")
+
+    assert not definition.defined_names()