diff --git a/jedi/cache.py b/jedi/cache.py
index 931ddf88..64252851 100644
--- a/jedi/cache.py
+++ b/jedi/cache.py
@@ -147,6 +147,21 @@ def underscore_memoization(func):
     return wrapper
 
 
+def memoize(func):
+    """A normal memoize function."""
+    dct = {}
+
+    def wrapper(*args, **kwargs):
+        key = (args, frozenset(kwargs.items()))
+        try:
+            return dct[key]
+        except KeyError:
+            result = func(*args, **kwargs)
+            dct[key] = result
+            return result
+    return wrapper
+
+
 def cache_star_import(func):
     def wrapper(evaluator, scope, *args, **kwargs):
         with common.ignored(KeyError):
diff --git a/jedi/evaluate/compiled/__init__.py b/jedi/evaluate/compiled/__init__.py
index 7a3eaf52..df82cbb8 100644
--- a/jedi/evaluate/compiled/__init__.py
+++ b/jedi/evaluate/compiled/__init__.py
@@ -8,7 +8,7 @@ import os
 
 from jedi._compatibility import builtins as _builtins, unicode
 from jedi import debug
-from jedi.cache import underscore_memoization
+from jedi.cache import underscore_memoization, memoize
 from jedi.evaluate.sys_path import get_sys_path
 from jedi.parser.representation import Param, SubModule, Base, IsScope, Operator
 from jedi.evaluate.helpers import FakeName
@@ -307,11 +307,13 @@ def _parse_function_doc(doc):
 
 
 class Builtin(CompiledObject, IsScope):
+    @memoize
     def get_defined_names(self):
         # Filter None, because it's really just a keyword, nobody wants to
         # access it.
         return [d for d in super(Builtin, self).get_defined_names() if d.name != 'None']
 
+    @memoize
     def get_by_name(self, name):
         item = [n for n in self.get_defined_names() if n.get_code() == name][0]
         return item.parent
diff --git a/test/test_speed.py b/test/test_speed.py
index be39cc08..dabc0d57 100644
--- a/test/test_speed.py
+++ b/test/test_speed.py
@@ -25,7 +25,7 @@ class TestSpeed(TestCase):
                     func(self)
                 single_time = (time.time() - first) / number
                 print('\nspeed', func, single_time)
-                assert single_time < time_per_run, 'Too slow.'
+                assert single_time < time_per_run
             return wrapper
         return decorated