diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index a17fcee..ee4e42f 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -730,6 +730,13 @@
         self.assertRaises(self.UnsupportedOperation, bufio.tell)
         self.assertRaises(self.UnsupportedOperation, bufio.seek, 0)
 
+    def test_readonly_attributes(self):
+        raw = self.MockRawIO()
+        buf = self.tp(raw)
+        x = self.MockRawIO()
+        with self.assertRaises(AttributeError):
+            buf.raw = x
+
 
 class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
     read_mode = "rb"
@@ -2245,6 +2252,12 @@
         self.assertRaises(self.UnsupportedOperation, txt.tell)
         self.assertRaises(self.UnsupportedOperation, txt.seek, 0)
 
+    def test_readonly_attributes(self):
+        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
+        buf = self.BytesIO(self.testdata)
+        with self.assertRaises(AttributeError):
+            txt.buffer = buf
+
 class CTextIOWrapperTest(TextIOWrapperTest):
 
     def test_initialization(self):