diff --git a/jedi/api/__init__.py b/jedi/api/__init__.py
index 1743451f..41c1f23c 100644
--- a/jedi/api/__init__.py
+++ b/jedi/api/__init__.py
@@ -116,7 +116,7 @@ class Script(object):
             code=source,
             path=self.path,
             cache=False,  # No disk cache, because the current script often changes.
-            diff_cache=True,
+            diff_cache=settings.fast_parser,
             cache_path=settings.cache_directory
         )
         debug.speed('parsed')
diff --git a/jedi/evaluate/compiled/mixed.py b/jedi/evaluate/compiled/mixed.py
index 773b5292..f2cb2152 100644
--- a/jedi/evaluate/compiled/mixed.py
+++ b/jedi/evaluate/compiled/mixed.py
@@ -107,7 +107,7 @@ def _load_module(evaluator, path):
     module_node = evaluator.grammar.parse(
         path=path,
         cache=True,
-        diff_cache=True,
+        diff_cache=settings.fast_parser,
         cache_path=settings.cache_directory
     ).get_root_node()
     # python_module = inspect.getmodule(python_object)
diff --git a/jedi/evaluate/imports.py b/jedi/evaluate/imports.py
index 17b450ad..df2f0fcc 100644
--- a/jedi/evaluate/imports.py
+++ b/jedi/evaluate/imports.py
@@ -500,7 +500,8 @@ def _load_module(evaluator, path=None, code=None, sys_path=None,
 
         if path is not None and path.endswith(('.py', '.zip', '.egg')):
             module_node = evaluator.parse(
-                code=code, path=path, cache=True, diff_cache=True,
+                code=code, path=path, cache=True,
+                diff_cache=settings.fast_parser,
                 cache_path=settings.cache_directory)
 
             from jedi.evaluate.context import ModuleContext