diff --git a/jedi/inference/syntax_tree.py b/jedi/inference/syntax_tree.py
index a4f3e1210..294fb7e4c 100644
--- a/jedi/inference/syntax_tree.py
+++ b/jedi/inference/syntax_tree.py
@@ -493,8 +493,10 @@ def infer_factor(value_set, operator):
         elif operator == 'not':
             b = value.py__bool__()
             if b is None:  # Uncertainty.
-                return
-            yield compiled.create_simple_object(value.inference_state, not b)
+                yield list(value.inference_state.builtins_module.py__getattribute__('bool')
+                           .execute_annotation()).pop()
+            else:
+                yield compiled.create_simple_object(value.inference_state, not b)
         else:
             yield value
 
@@ -645,10 +647,7 @@ def _infer_comparison_part(inference_state, context, left, operator, right):
             _bool_to_value(inference_state, False)
         ])
     elif str_operator in ('in', 'not in'):
-        return ValueSet([
-            _bool_to_value(inference_state, True),
-            _bool_to_value(inference_state, False)
-        ])
+        return inference_state.builtins_module.py__getattribute__('bool').execute_annotation()
 
     def check(obj):
         """Checks if a Jedi object is either a float or an int."""
diff --git a/test/completion/basic.py b/test/completion/basic.py
index 3c0448e59..2894b0e89 100644
--- a/test/completion/basic.py
+++ b/test/completion/basic.py
@@ -431,3 +431,6 @@ def __enter__(self):
 
 #? bool()
 res = 'f' in 'foo'; res
+
+#? bool()
+res = not {}; res