diff -r 5a6fa1b8767f Lib/test/test_mmap.py
--- a/Lib/test/test_mmap.py	Wed Apr 11 16:46:54 2012 -0400
+++ b/Lib/test/test_mmap.py	Sat Sep 08 11:01:43 2012 -0400
@@ -466,6 +466,22 @@
         f.flush ()
         return mmap.mmap (f.fileno(), 0)
 
+    def test_empty_file (self):
+        f = open (TESTFN, 'w+b')
+        f.close()
+        f = open(TESTFN, "rb")
+        try:
+            m = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
+            m.close()
+            f.close()
+            self.fail("should not have been able to mmap empty file")
+        except ValueError as e:
+            f.close()
+            self.assertEqual(str(e), "cannot mmap an empty file")
+        except:
+            f.close()
+            self.fail("unexpected exception: " + str(e))
+
     def test_offset (self):
         f = open (TESTFN, 'w+b')
 
diff -r 5a6fa1b8767f Modules/mmapmodule.c
--- a/Modules/mmapmodule.c	Wed Apr 11 16:46:54 2012 -0400
+++ b/Modules/mmapmodule.c	Sat Sep 08 11:01:43 2012 -0400
@@ -1109,6 +1109,11 @@
 #  endif
     if (fd != -1 && fstat(fd, &st) == 0 && S_ISREG(st.st_mode)) {
         if (map_size == 0) {
+            if (st.st_size == 0) {
+                PyErr_SetString(PyExc_ValueError,
+                                "cannot mmap an empty file");
+                return NULL;
+            }
             if (offset >= st.st_size) {
                 PyErr_SetString(PyExc_ValueError,
                                 "mmap offset is greater than file size");