diff -r d4e73dff92fc Lib/test/test_memoryview.py
--- a/Lib/test/test_memoryview.py	Tue Jan 18 01:30:24 2011 +0100
+++ b/Lib/test/test_memoryview.py	Tue Jan 18 18:47:45 2011 +0200
@@ -9,6 +9,7 @@
 import gc
 import weakref
 import array
+import io
 
 
 class AbstractMemoryTests:
@@ -202,6 +203,14 @@
             m = None
             self.assertEqual(sys.getrefcount(b), oldrefcount)
 
+    def test_issue10451(self):
+        # issue10451: memoryview incorrectly exposes a readonly
+        # buffer as writable causing a segfault if using mmap
+        b = b"XXXX"
+        m = memoryview(b)
+        i = io.BytesIO(b'ZZZZ')
+        self.assertRaises(TypeError, i.readinto, m)
+
     def test_gc(self):
         for tp in self._types:
             if not isinstance(tp, type):
diff -r d4e73dff92fc Objects/memoryobject.c
--- a/Objects/memoryobject.c	Tue Jan 18 01:30:24 2011 +0100
+++ b/Objects/memoryobject.c	Tue Jan 18 18:47:45 2011 +0200
@@ -52,9 +52,6 @@
 {
     int res = 0;
     CHECK_RELEASED_INT(self);
-    /* XXX for whatever reason fixing the flags seems necessary */
-    if (self->view.readonly)
-        flags &= ~PyBUF_WRITABLE;
     if (self->view.obj != NULL)
         res = PyObject_GetBuffer(self->view.obj, view, flags);
     if (view)