diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 5bda935..230dbf4 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -453,6 +453,11 @@
 class BytesTest(BaseBytesTest):
     type2test = bytes
 
+    def test_buffer_is_readonly(self):
+        with open(sys.stdin.fileno(), "rb", buffering=0) as f:
+            self.assertRaises(TypeError, f.readinto, b"")
+
+
 class ByteArrayTest(BaseBytesTest):
     type2test = bytearray
 
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 222c42c..9d753b7 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1112,7 +1112,7 @@
         SocketConnectedTest.__init__(self, methodName=methodName)
 
     def testRecvInto(self):
-        buf = b" "*1024
+        buf = bytearray(1024)
         nbytes = self.cli_conn.recv_into(buf)
         self.assertEqual(nbytes, len(MSG))
         msg = buf[:len(MSG)]
@@ -1123,7 +1123,7 @@
         self.serv_conn.send(buf)
 
     def testRecvFromInto(self):
-        buf = b" "*1024
+        buf = bytearray(1024)
         nbytes, addr = self.cli_conn.recvfrom_into(buf)
         self.assertEqual(nbytes, len(MSG))
         msg = buf[:len(MSG)]