diff --git a/Lib/test/test_xdrlib.py b/Lib/test/test_xdrlib.py
index d0fb1e5..44d5a82 100644
--- a/Lib/test/test_xdrlib.py
+++ b/Lib/test/test_xdrlib.py
@@ -8,8 +8,8 @@
     def test_xdr(self):
         p = xdrlib.Packer()
 
-        s = 'hello world'
-        a = ['what', 'is', 'hapnin', 'doctor']
+        s = b'hello world'
+        a = [b'what', b'is', b'hapnin', b'doctor']
 
         p.pack_int(42)
         p.pack_uint(9)
diff --git a/Lib/xdrlib.py b/Lib/xdrlib.py
index 055ee82..98bdedb 100644
--- a/Lib/xdrlib.py
+++ b/Lib/xdrlib.py
@@ -5,7 +5,7 @@
 """
 
 import struct
-from io import StringIO as _StringIO
+from io import BytesIO
 
 __all__ = ["Error", "Packer", "Unpacker", "ConversionError"]
 
@@ -40,7 +40,7 @@
         self.reset()
 
     def reset(self):
-        self.__buf = _StringIO()
+        self.__buf = BytesIO()
 
     def get_buffer(self):
         return self.__buf.getvalue()
@@ -54,8 +54,8 @@
     pack_enum = pack_int
 
     def pack_bool(self, x):
-        if x: self.__buf.write('\0\0\0\1')
-        else: self.__buf.write('\0\0\0\0')
+        if x: self.__buf.write(b'\0\0\0\1')
+        else: self.__buf.write(b'\0\0\0\0')
 
     def pack_uhyper(self, x):
         self.pack_uint(x>>32 & 0xffffffff)
@@ -78,7 +78,7 @@
             raise ValueError, 'fstring size must be nonnegative'
         data = s[:n]
         n = ((n+3)//4)*4
-        data = data + (n - len(data)) * '\0'
+        data = data + (n - len(data)) * b'\0'
         self.__buf.write(data)
 
     pack_fopaque = pack_fstring