diff --git a/jedi/evaluate/imports.py b/jedi/evaluate/imports.py
index ecd3a261..3e91b1e4 100644
--- a/jedi/evaluate/imports.py
+++ b/jedi/evaluate/imports.py
@@ -331,7 +331,7 @@ class _Importer(object):
                     new = os.path.sep.join(parts[:i])
                     in_path.append(new)
 
-        return in_path + sys_path.sys_path_with_modifications(self.module)
+        return in_path + sys_path.sys_path_with_modifications(self._evaluator, self.module)
 
     def follow(self, evaluator):
         scope, rest = self.follow_file_system()
diff --git a/jedi/evaluate/sys_path.py b/jedi/evaluate/sys_path.py
index 2390fd1b..bd5b6583 100644
--- a/jedi/evaluate/sys_path.py
+++ b/jedi/evaluate/sys_path.py
@@ -3,6 +3,7 @@ import sys
 
 from jedi._compatibility import exec_function, unicode
 from jedi.parser import representation as pr
+from jedi.evaluate.cache import memoize_default
 from jedi import debug
 from jedi import common
 
@@ -22,8 +23,8 @@ def get_sys_path():
     return [p for p in sys.path if p != ""]
 
 
-#@cache.memoize_default([]) TODO add some sort of cache again.
-def sys_path_with_modifications(module):
+@memoize_default(evaluator_is_first_arg=True)
+def sys_path_with_modifications(evaluator, module):
     def execute_code(code):
         c = "import os; from os.path import *; result=%s"
         variables = {'__file__': module.path}