diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index c8e52a6..1ad611d 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -499,6 +499,34 @@
         m.seek(8)
         self.assertRaises(ValueError, m.write, "bar")
 
+    if os.name == 'nt':
+        def test_tagname(self):
+            data1 = "0123456789"
+            data2 = "abcdefghij"
+            assert len(data1) == len(data2)
+            # Test same tag
+            m1 = mmap.mmap(-1, len(data1), tagname="foo")
+            m1[:] = data1
+            m2 = mmap.mmap(-1, len(data2), tagname="foo")
+            m2[:] = data2
+            self.assertEquals(m1[:], data2)
+            self.assertEquals(m2[:], data2)
+            # Test differnt tag
+            m1 = mmap.mmap(-1, len(data1), tagname="foo")
+            m1[:] = data1
+            m2 = mmap.mmap(-1, len(data2), tagname="boo")
+            m2[:] = data2
+            self.assertEquals(m1[:], data1)
+            self.assertEquals(m2[:], data2)
+
+        def test_tagname_crash(self):
+            # Should not crash (Issue 1733986)
+            m = mmap.mmap(-1, 1000, tagname="foo")
+            try:
+                mmap.mmap(-1, 5000, tagname="foo")[:] # same tagname, but larger size
+            except:
+                pass
+
 
 def test_main():
     run_unittest(MmapTests)
diff --git a/Misc/NEWS b/Misc/NEWS
index 3553dbc..f2bebd6 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -89,6 +89,9 @@
 Library
 -------
 
+- Issue #1733986: Fixed mmap crash in accessing elements of second map object
+  with same tagname but larger size than first map. (Windows)
+
 - Issue #5386: mmap.write_byte didn't check map size, so it could cause buffer
   overrun.
 
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 8407c11..ca5fa88 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -1373,7 +1373,7 @@
 						     dwDesiredAccess,
 						     off_hi,
 						     off_lo,
-						     0);
+						     m_obj->size);
 		if (m_obj->data != NULL)
 			return (PyObject *)m_obj;
 		else