diff -r a7e0a1dbfbb6 Lib/test/test_xdrlib.py
--- a/Lib/test/test_xdrlib.py	Sun Mar 27 10:15:57 2011 +0200
+++ b/Lib/test/test_xdrlib.py	Sun Mar 27 12:41:09 2011 +0200
@@ -9,6 +9,7 @@
         p = xdrlib.Packer()
 
         s = b'hello world'
+        u = 'hello world'
         a = [b'what', b'is', b'hapnin', b'doctor']
 
         p.pack_int(42)
@@ -19,6 +20,7 @@
         p.pack_float(1.9)
         p.pack_double(1.9)
         p.pack_string(s)
+        p.pack_string(u)
         p.pack_list(range(5), p.pack_uint)
         p.pack_array(a, p.pack_string)
 
@@ -44,6 +46,7 @@
         self.assertAlmostEqual(up.unpack_float(), 1.9)
         self.assertAlmostEqual(up.unpack_double(), 1.9)
         self.assertEqual(up.unpack_string(), s)
+        self.assertEqual(up.unpack_string().decode('UTF-8'), u)
         self.assertEqual(up.unpack_list(up.unpack_uint), list(range(5)))
         self.assertEqual(up.unpack_array(up.unpack_string), a)
         up.done()
diff -r a7e0a1dbfbb6 Lib/xdrlib.py
--- a/Lib/xdrlib.py	Sun Mar 27 10:15:57 2011 +0200
+++ b/Lib/xdrlib.py	Sun Mar 27 12:41:09 2011 +0200
@@ -76,6 +76,8 @@
     def pack_fstring(self, n, s):
         if n < 0:
             raise ValueError('fstring size must be nonnegative')
+        if isinstance(s, str):
+            s = bytes(s, 'UTF-8')
         data = s[:n]
         n = ((n+3)//4)*4
         data = data + (n - len(data)) * b'\0'