diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index fa00eb4..5474a4e 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -556,7 +556,11 @@
             if not data:
                 break
             res += data
-        return bytes(res)
+        if res:
+            return bytes(res)
+        else:
+            # b'' or None
+            return data
 
     def readinto(self, b):
         """Read up to len(b) bytes into b.
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 109c82d..5333bb6 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -790,14 +790,17 @@
         # Inject some None's in there to simulate EWOULDBLOCK
         rawio = self.MockRawIO((b"abc", b"d", None, b"efg", None, None, None))
         bufio = self.tp(rawio)
-
         self.assertEqual(b"abcd", bufio.read(6))
         self.assertEqual(b"e", bufio.read(1))
         self.assertEqual(b"fg", bufio.read())
         self.assertEqual(b"", bufio.peek(1))
-        self.assertTrue(None is bufio.read())
+        self.assertIsNone(bufio.read())
         self.assertEqual(b"", bufio.read())
 
+        rawio = self.MockRawIO((b"a", None, None))
+        self.assertEqual(b"a", rawio.readall())
+        self.assertIsNone(rawio.readall())
+
     def test_read_past_eof(self):
         rawio = self.MockRawIO((b"abc", b"d", b"efg"))
         bufio = self.tp(rawio)