diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index bbf65bc..5458f99 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1924,8 +1924,10 @@
         # C version, even under Windows.
         if newline is None:
             self._writetranslate = False
-        if initial_value:
+        if initial_value is not None:
             if not isinstance(initial_value, str):
+                raise TypeError("initial_value must be str or None, not {0}"
+                                .format(type(initial_value).__name__))
                 initial_value = str(initial_value)
             self.write(initial_value)
             self.seek(0)
diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
index 0b25283..670dab9 100644
--- a/Lib/test/test_memoryio.py
+++ b/Lib/test/test_memoryio.py
@@ -140,6 +140,7 @@
         self.assertEqual(memio.getvalue(), buf * 2)
         memio.__init__(buf)
         self.assertEqual(memio.getvalue(), buf)
+        self.assertRaises(TypeError, memio.__init__, [])
 
     def test_read(self):
         buf = self.buftype("1234567890")
@@ -530,6 +531,13 @@
         memio = self.ioclass("a\r\nb\r\n", newline=None)
         self.assertEqual(memio.read(5), "a\nb\n")
 
+    def test_newline_argument(self):
+        self.assertRaises(TypeError, self.ioclass, newline=b"\n")
+        self.assertRaises(ValueError, self.ioclass, newline="error")
+        # These should not raise an error
+        for newline in (None, "", "\n", "\r", "\r\n"):
+            self.ioclass(newline=newline)
+
 
 class CBytesIOTest(PyBytesIOTest):
     ioclass = io.BytesIO