diff --git a/jedi/evaluate/iterable.py b/jedi/evaluate/iterable.py
index c566b0aa..a2ad747a 100644
--- a/jedi/evaluate/iterable.py
+++ b/jedi/evaluate/iterable.py
@@ -654,6 +654,7 @@ def py__iter__types(evaluator, types, node=None):
 
 def py__getitem__(evaluator, context, types, trailer):
     from jedi.evaluate.representation import ClassContext
+    from jedi.evaluate.instance import TreeInstance
     result = set()
 
     trailer_op, node, trailer_cl = trailer.children
@@ -663,7 +664,7 @@ def py__getitem__(evaluator, context, types, trailer):
     # special case: PEP0484 typing module, see
     # https://github.com/davidhalter/jedi/issues/663
     for typ in list(types):
-        if isinstance(typ, ClassContext):
+        if isinstance(typ, (ClassContext, TreeInstance)):
             typing_module_types = pep0484.py__getitem__(context, typ, node)
             if typing_module_types is not None:
                 types.remove(typ)
diff --git a/jedi/evaluate/pep0484.py b/jedi/evaluate/pep0484.py
index 28b344eb..d066e549 100644
--- a/jedi/evaluate/pep0484.py
+++ b/jedi/evaluate/pep0484.py
@@ -139,9 +139,13 @@ def py__getitem__(context, typ, node):
     type_name = typ.name.string_name
 
     # hacked in Union and Optional, since it's hard to do nicely in parsed code
-    if type_name == "Union":
+    if type_name in ("Union", '_Union'):
+        # In Python 3.6 it's still called typing.Union but it's an instance
+        # called _Union.
         return unite(context.eval_node(node) for node in nodes)
-    if type_name == "Optional":
+    if type_name in ("Optional", '_Optional'):
+        # Here we have the same issue like in Union. Therefore we also need to
+        # check for the instance typing._Optional (Python 3.6).
         return context.eval_node(nodes[0])
 
     from jedi.evaluate.representation import ModuleContext