diff -r 588657f910ac Lib/test/test_xdrlib.py
--- a/Lib/test/test_xdrlib.py	Thu Oct 09 13:53:45 2014 +0200
+++ b/Lib/test/test_xdrlib.py	Thu Oct 09 18:17:08 2014 +0300
@@ -51,8 +51,32 @@
         up.done()
         self.assertRaises(EOFError, up.unpack_uint)
 
+class ConversionErrorTest(unittest.TestCase):
+
+    def setUp(self):
+        self.packer = xdrlib.Packer()
+
+    def assertRaisesConversion(self, *args):
+        self.assertRaises(xdrlib.ConversionError, *args)
+
+    def test_pack_int(self):
+        self.assertRaisesConversion(self.packer.pack_int, 'string')
+
+    def test_pack_uint(self):
+        self.assertRaisesConversion(self.packer.pack_uint, 'string')
+
+    def test_float(self):
+        self.assertRaisesConversion(self.packer.pack_float, 'string')
+
+    def test_double(self):
+        self.assertRaisesConversion(self.packer.pack_double, 'string')
+
+    def test_uhyper(self):
+        self.assertRaisesConversion(self.packer.pack_uhyper, 'string')
+
 def test_main():
     support.run_unittest(XDRTest)
+    support.run_unittest(ConversionErrorTest)
 
 if __name__ == "__main__":
     test_main()
diff -r 588657f910ac Lib/xdrlib.py
--- a/Lib/xdrlib.py	Thu Oct 09 13:53:45 2014 +0200
+++ b/Lib/xdrlib.py	Thu Oct 09 18:17:08 2014 +0300
@@ -6,6 +6,7 @@
 
 import struct
 from io import BytesIO
+from functools import wraps
 
 __all__ = ["Error", "Packer", "Unpacker", "ConversionError"]
 
@@ -31,6 +32,16 @@
 class ConversionError(Error):
     pass
 
+def raise_conversion_error(function):
+    """ Wrap any raised struct.errors in a ConversionError. """
+
+    @wraps(function)
+    def result(self, value):
+        try:
+            return function(self, value)
+        except struct.error as e:
+            raise ConversionError(e.args[0]) from None
+    return result
 
 
 class Packer:
@@ -47,9 +58,11 @@
     # backwards compatibility
     get_buf = get_buffer
 
+    @raise_conversion_error
     def pack_uint(self, x):
         self.__buf.write(struct.pack('>L', x))
 
+    @raise_conversion_error
     def pack_int(self, x):
         self.__buf.write(struct.pack('>l', x))
 
@@ -60,20 +73,24 @@
         else: self.__buf.write(b'\0\0\0\0')
 
     def pack_uhyper(self, x):
-        self.pack_uint(x>>32 & 0xffffffff)
-        self.pack_uint(x & 0xffffffff)
+        try:
+            self.pack_uint(x>>32 & 0xffffffff)
+        except (TypeError, struct.error) as e:
+            raise ConversionError(e.args[0]) from None
+        try:
+            self.pack_uint(x & 0xffffffff)
+        except (TypeError, struct.error) as e:
+            raise ConversionError(e.args[0]) from None
 
     pack_hyper = pack_uhyper
 
+    @raise_conversion_error
     def pack_float(self, x):
-        try: self.__buf.write(struct.pack('>f', x))
-        except struct.error as msg:
-            raise ConversionError(msg)
+        self.__buf.write(struct.pack('>f', x))
 
+    @raise_conversion_error
     def pack_double(self, x):
-        try: self.__buf.write(struct.pack('>d', x))
-        except struct.error as msg:
-            raise ConversionError(msg)
+        self.__buf.write(struct.pack('>d', x))
 
     def pack_fstring(self, n, s):
         if n < 0: