diff -r ffcb7f5f2e48 Lib/test/test_mmap.py
--- a/Lib/test/test_mmap.py	Fri Sep 07 02:26:26 2012 +0200
+++ b/Lib/test/test_mmap.py	Sun Sep 09 16:13:50 2012 -0400
@@ -488,6 +488,15 @@
         f.flush ()
         return mmap.mmap (f.fileno(), 0)
 
+    def test_empty_file (self):
+        f = open (TESTFN, 'w+b')
+        f.close()
+        f = open(TESTFN, "rb")
+        self.assertRaisesRegex(ValueError,
+                               "cannot mmap an empty file",
+                               mmap.mmap, f.fileno(), 0, access=mmap.ACCESS_READ)
+        f.close()
+
     def test_offset (self):
         f = open (TESTFN, 'w+b')
 
diff -r ffcb7f5f2e48 Modules/mmapmodule.c
--- a/Modules/mmapmodule.c	Fri Sep 07 02:26:26 2012 +0200
+++ b/Modules/mmapmodule.c	Sun Sep 09 16:13:50 2012 -0400
@@ -1163,6 +1163,11 @@
     if (fd != -1 && fstat(fd, &st) == 0 && S_ISREG(st.st_mode)) {
         if (map_size == 0) {
             off_t calc_size;
+            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");