diff -r fbe29ca8192b Lib/test/test_dict.py
--- a/Lib/test/test_dict.py	Tue Sep 13 13:27:41 2016 +0200
+++ b/Lib/test/test_dict.py	Tue Sep 13 22:10:43 2016 +0800
@@ -874,7 +874,7 @@
     @support.cpython_only
     def test_splittable_pop(self):
         """split table must be combined when d.pop(k)"""
-        a, b = self.make_shared_key_dict(2)
+        a, b, c = self.make_shared_key_dict(3)
 
         orig_size = sys.getsizeof(a)
 
@@ -891,6 +891,11 @@
         self.assertEqual(list(a), ['x', 'z', 'y'])
         self.assertEqual(list(b), ['x', 'y', 'z'])
 
+        # issue 28120
+        c['a'] = 4
+        with self.assertRaises(KeyError):
+            b.pop('a')
+
     @support.cpython_only
     def test_splittable_popitem(self):
         """split table must be combined when d.popitem()"""
diff -r fbe29ca8192b Objects/dictobject.c
--- a/Objects/dictobject.c	Tue Sep 13 13:27:41 2016 +0200
+++ b/Objects/dictobject.c	Tue Sep 13 22:10:43 2016 +0800
@@ -1721,7 +1721,7 @@
     ix = (mp->ma_keys->dk_lookup)(mp, key, hash, &value_addr, &hashpos);
     if (ix == DKIX_ERROR)
         return NULL;
-    if (ix == DKIX_EMPTY) {
+    if (ix == DKIX_EMPTY || *value_addr == NULL) {
         if (deflt) {
             Py_INCREF(deflt);
             return deflt;