diff --git a/test/test_persistent_dict.py b/test/test_persistent_dict.py
index 61338d2a7b15787a52dbbe4773f12f8eaf197cf9..bea880807a12c636ec840194c5f4b56bbefb12f9 100644
--- a/test/test_persistent_dict.py
+++ b/test/test_persistent_dict.py
@@ -261,11 +261,15 @@ def test_write_once_persistent_dict_cache_collisions():
         key2 = PDictTestingKeyOrValue(2, hash_key=0)
         pdict[key1] = 1
 
+        # check lookup        
         with pytest.warns(UserWarning):
-            # check lookup
             with pytest.raises(NoSuchEntryError):
                 pdict[key2]
 
+        # check update
+        with pytest.raises(ReadOnlyEntryError):
+            pdict[key2] = 1
+
     finally:
         shutil.rmtree(tmpdir)