2 files changed, 6 insertions, 0 deletions
diff --git a/Misc/NEWS b/Misc/NEWS
index 1889478..15c0bb3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -87,6 +87,8 @@ Library
 Extensions
 ----------
 
+- Issue #678250: Make mmap flush a noop on ACCESS_READ and ACCESS_COPY.
+
 - Issue #9054: Fix a crash occurring when using the pyexpat module
   with expat version 2.0.1.
 
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 3413f17..680f1f1 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -569,6 +569,10 @@ mmap_flush_method(mmap_object *self, PyObject *args)
         PyErr_SetString(PyExc_ValueError, "flush values out of range");
         return NULL;
     }
+
+    if (self->access == ACCESS_READ || self->access == ACCESS_COPY)
+        return PyLong_FromLong(0);
+
 #ifdef MS_WINDOWS
     return PyLong_FromLong((long) FlushViewOfFile(self->data+offset, size));
 #elif defined(UNIX)