diff -r 14be8f02e694 Lib/test/test_mmap.py
--- a/Lib/test/test_mmap.py	Sat Jan 15 06:53:33 2011 +0100
+++ b/Lib/test/test_mmap.py	Sat Jan 15 17:12:21 2011 +0200
@@ -320,6 +320,21 @@
             mf.close()
             f.close()
 
+    def test_length_0_offset(self):
+        # test mapping of remainder of file by passing 0 for map length
+        # with an offset doesn't cause a segfault.
+        if hasattr(os, "stat"):
+            f = open(TESTFN, "wb+")
+
+            f.write(49152 * b'm') # Arbitrary character
+            f.close()
+
+            f = open(TESTFN, "rb")
+            mf = mmap.mmap(f.fileno(), 0, offset=40960, access=mmap.ACCESS_READ)
+            self.assertRaises(IndexError, mf.__getitem__, 45000)
+            mf.close()
+            f.close()
+
     def test_move(self):
         # make move works everywhere (64-bit format problem earlier)
         f = open(TESTFN, 'wb+')
diff -r 14be8f02e694 Modules/mmapmodule.c
--- a/Modules/mmapmodule.c	Sat Jan 15 06:53:33 2011 +0100
+++ b/Modules/mmapmodule.c	Sat Jan 15 17:12:21 2011 +0200
@@ -1116,7 +1116,7 @@
 #  endif
     if (fd != -1 && fstat(fd, &st) == 0 && S_ISREG(st.st_mode)) {
         if (map_size == 0) {
-            map_size = st.st_size;
+            map_size = st.st_size - offset;
         } else if ((size_t)offset + (size_t)map_size > st.st_size) {
             PyErr_SetString(PyExc_ValueError,
                             "mmap length is greater than file size");