diff --git a/parso/cache.py b/parso/cache.py
index bc9cef0..cc9e4ee 100644
--- a/parso/cache.py
+++ b/parso/cache.py
@@ -155,7 +155,7 @@ def _get_hashed_path(grammar, path, cache_path=None):
     directory = _get_cache_directory_path(cache_path=cache_path)
 
     file_hash = hashlib.sha256(path.encode("utf-8")).hexdigest()
-    return os.path.join(directory, '%s-%s.pkl' % (grammar.sha256, file_hash))
+    return os.path.join(directory, '%s-%s.pkl' % (grammar._sha256, file_hash))
 
 
 def _get_cache_directory_path(cache_path=None):
diff --git a/parso/grammar.py b/parso/grammar.py
index e61660c..927696c 100644
--- a/parso/grammar.py
+++ b/parso/grammar.py
@@ -9,7 +9,7 @@ class Grammar(object):
         self._parser = parser
         self._tokenizer = tokenizer
         self._diff_parser = diff_parser
-        self.sha256 = hashlib.sha256(bnf_text.encode("utf-8")).hexdigest()
+        self._sha256 = hashlib.sha256(bnf_text.encode("utf-8")).hexdigest()
 
     def __repr__(self):
         labels = self._pgen_grammar.symbol2number.values()