diff --git a/jedi/api/__init__.py b/jedi/api/__init__.py
index 5e0d6d4e..648c12eb 100644
--- a/jedi/api/__init__.py
+++ b/jedi/api/__init__.py
@@ -131,6 +131,7 @@ class Script(object):
         self._evaluator = Evaluator(self._grammar, sys_path=sys_path)
         debug.speed('init')
 
+    @cache.memoize_method
     def _get_module(self):
         cache.invalidate_star_import_cache(self._path)
         parser = FastParser(self._grammar, self._source, self.path)
diff --git a/test/test_parser/test_diff_parser.py b/test/test_parser/test_diff_parser.py
index 2c9d6251..0bc58f01 100644
--- a/test/test_parser/test_diff_parser.py
+++ b/test/test_parser/test_diff_parser.py
@@ -31,12 +31,18 @@ def test_add_to_end():
 
     b = "    def h(self):\n" \
         "        self."
-    assert jedi.Script(a, 7, 12, 'example.py').completions()
-    assert jedi.Script(a + b, path='example.py').completions()
+
+    def complete(code, line=None, column=None):
+        script = jedi.Script(code, line, column, 'example.py')
+        assert script.completions()
+        _assert_valid_graph(script._get_module())
+
+    complete(a, 7, 12)
+    complete(a + b)
 
     a = a[:-1] + '.\n'
-    assert jedi.Script(a, 7, 13, 'example.py').completions()
-    assert jedi.Script(a + b, path='example.py').completions()
+    complete(a, 7, 13)
+    complete(a + b)
 
 
 def _check_error_leaves_nodes(node):