diff --git a/Lib/test/test_defaultdict.py b/Lib/test/test_defaultdict.py
index 5935e05..7ad2392 100644
--- a/Lib/test/test_defaultdict.py
+++ b/Lib/test/test_defaultdict.py
@@ -59,6 +59,7 @@
         d1 = defaultdict()
         self.assertEqual(d1.default_factory, None)
         self.assertEqual(repr(d1), "defaultdict(None, {})")
+        self.assertEqual(eval(repr(d1)), d1)
         d1[11] = 41
         self.assertEqual(repr(d1), "defaultdict(None, {11: 41})")
         d2 = defaultdict(int)
@@ -111,6 +112,12 @@
         d4[12]
         self.assertEqual(d4, {42: [], 12: []})
 
+        # Issue 6637: Copy fails for empty default dict
+        d = defaultdict()
+        d['a'] = 42
+        e = d.copy()
+        self.assertEqual(e['a'], 42)
+
     def test_shallow_copy(self):
         d1 = defaultdict(foobar, {1: 1})
         d2 = copy.copy(d1)
diff --git a/Misc/NEWS b/Misc/NEWS
index a9cb534..289ee1d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -70,6 +70,10 @@
 Library
 -------
 
+- Issue #6637: defaultdict.copy() did not work when the default factory
+  was left unspecified.  Also, the eval/repr round-trip would fail when
+  the default_factory was None.
+
 - Issue #1424152: Fix for httplib, urllib2 to support SSL while working through
   proxy. Original patch by Christopher Li, changes made by Senthil Kumaran.
 
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 0029532..faf033e 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1191,6 +1191,9 @@
 	   whose class constructor has the same signature.  Subclasses that
 	   define a different constructor signature must override copy().
 	*/
+
+	if (dd->default_factory == NULL)
+		return PyObject_CallFunctionObjArgs((PyObject*)Py_TYPE(dd), Py_None, dd, NULL);
 	return PyObject_CallFunctionObjArgs((PyObject*)Py_TYPE(dd),
 					    dd->default_factory, dd, NULL);
 }
@@ -1354,7 +1357,7 @@
 		Py_ssize_t n = PyTuple_GET_SIZE(args);
 		if (n > 0) {
 			newdefault = PyTuple_GET_ITEM(args, 0);
-			if (!PyCallable_Check(newdefault)) {
+			if (!PyCallable_Check(newdefault) && newdefault != Py_None) {
 				PyErr_SetString(PyExc_TypeError,
 					"first argument must be callable");                           
 				return -1;