diff --git a/IPython/config/loader.py b/IPython/config/loader.py
index 3cbd132..4786e35 100644
--- a/IPython/config/loader.py
+++ b/IPython/config/loader.py
@@ -24,7 +24,7 @@ import sys
 
 from IPython.external import argparse
 from IPython.utils.path import filefind, get_ipython_dir
-from IPython.utils import py3compat, warn
+from IPython.utils import py3compat, text, warn
 
 #-----------------------------------------------------------------------------
 # Exceptions
@@ -425,7 +425,7 @@ class KeyValueConfigLoader(CommandLineConfigLoader):
         """decode argv if bytes, using stin.encoding, falling back on default enc"""
         uargv = []
         if enc is None:
-            enc = sys.stdin.encoding or sys.getdefaultencoding()
+            enc = text.getdefaultencoding()
         for arg in argv:
             if not isinstance(arg, unicode):
                 # only decode if not already decoded
@@ -586,7 +586,8 @@ class ArgParseConfigLoader(CommandLineConfigLoader):
     def _parse_args(self, args):
         """self.parser->self.parsed_data"""
         # decode sys.argv to support unicode command-line options
-        uargs = [py3compat.cast_unicode(a) for a in args]
+        enc = text.getdefaultencoding()
+        uargs = [py3compat.cast_unicode(a, enc) for a in args]
         self.parsed_data, self.extra_args = self.parser.parse_known_args(uargs)
 
     def _convert_to_config(self):
diff --git a/IPython/utils/_process_win32.py b/IPython/utils/_process_win32.py
index 3a273c0..f1dd502 100644
--- a/IPython/utils/_process_win32.py
+++ b/IPython/utils/_process_win32.py
@@ -23,6 +23,7 @@ from subprocess import STDOUT
 
 # our own imports
 from ._process_common import read_no_interrupt, process_handler
+from . import text
 
 #-----------------------------------------------------------------------------
 # Function definitions
@@ -88,7 +89,7 @@ def _find_cmd(cmd):
 
 def _system_body(p):
     """Callback for _system."""
-    enc = sys.stdin.encoding or sys.getdefaultencoding()
+    enc = text.getdefaultencoding()
     for line in read_no_interrupt(p.stdout).splitlines():
         line = line.decode(enc, 'replace')
         print(line, file=sys.stdout)
diff --git a/IPython/utils/jsonutil.py b/IPython/utils/jsonutil.py
index 06ccb3d..52ac240 100644
--- a/IPython/utils/jsonutil.py
+++ b/IPython/utils/jsonutil.py
@@ -17,6 +17,7 @@ import types
 from datetime import datetime
 
 from IPython.utils import py3compat
+from IPython.utils import text
 next_attr_name = '__next__' if py3compat.PY3 else 'next'
 
 #-----------------------------------------------------------------------------
@@ -134,7 +135,7 @@ def json_clean(obj):
         return obj
     
     if isinstance(obj, bytes):
-        return obj.decode(sys.getdefaultencoding(), 'replace')
+        return obj.decode(text.getdefaultencoding(), 'replace')
     
     if isinstance(obj, container_to_list) or (
         hasattr(obj, '__iter__') and hasattr(obj, next_attr_name)):
diff --git a/IPython/utils/text.py b/IPython/utils/text.py
index bf4a143..dfe9454 100644
--- a/IPython/utils/text.py
+++ b/IPython/utils/text.py
@@ -16,9 +16,11 @@ Utilities for working with strings and text.
 
 import __main__
 
+import locale
 import os
 import re
 import shutil
+import sys
 import textwrap
 from string import Formatter
 
@@ -31,6 +33,28 @@ from IPython.utils.data import flatten
 # Code
 #-----------------------------------------------------------------------------
 
+# Less conservative replacement for sys.getdefaultencoding, that will try
+# to match the environment.
+# Defined here as central function, so if we find better choices, we
+# won't need to make changes all over IPython.
+def getdefaultencoding():
+    """Return IPython's guess for the default encoding for bytes as text.
+    
+    Asks for stdin.encoding first, to match the calling Terminal, but that
+    is often None for subprocesses.  Fall back on locale.getpreferredencoding()
+    which should be a sensible platform default (that respects LANG environment),
+    and finally to sys.getdefaultencoding() which is the most conservative option,
+    and usually ASCII.
+    """
+    enc = sys.stdin.encoding
+    if not enc:
+        try:
+            # There are reports of getpreferredencoding raising errors
+            # in some cases, which may well be fixed, but let's be conservative here.
+            enc = locale.getpreferredencoding(False)
+        except Exception:
+            pass
+    return enc or sys.getdefaultencoding()
 
 def unquote_ends(istr):
     """Remove a single pair of quotes from the endpoints of a string."""
diff --git a/IPython/zmq/iostream.py b/IPython/zmq/iostream.py
index 5fcfb98..8579398 100644
--- a/IPython/zmq/iostream.py
+++ b/IPython/zmq/iostream.py
@@ -4,7 +4,7 @@ from io import StringIO
 
 from session import extract_header, Message
 
-from IPython.utils import io
+from IPython.utils import io, text
 
 #-----------------------------------------------------------------------------
 # Globals
@@ -69,7 +69,7 @@ class OutStream(object):
         else:
             # Make sure that we're handling unicode
             if not isinstance(string, unicode):
-                enc = sys.stdin.encoding or sys.getdefaultencoding()
+                enc = text.getdefaultencoding()
                 string = string.decode(enc, 'replace')
             
             self._buffer.write(string)
diff --git a/IPython/zmq/ipkernel.py b/IPython/zmq/ipkernel.py
index 264d6b1..0df9093 100755
--- a/IPython/zmq/ipkernel.py
+++ b/IPython/zmq/ipkernel.py
@@ -303,6 +303,7 @@ class Kernel(Configurable):
             time.sleep(self._execute_sleep)
         
         # Send the reply.
+        reply_content = json_clean(reply_content)
         reply_msg = self.session.send(self.shell_socket, u'execute_reply',
                                       reply_content, parent, ident=ident)
         self.log.debug(str(reply_msg))
@@ -321,6 +322,7 @@ class Kernel(Configurable):
         matches = {'matches' : matches,
                    'matched_text' : txt,
                    'status' : 'ok'}
+        matches = json_clean(matches)
         completion_msg = self.session.send(self.shell_socket, 'complete_reply',
                                            matches, parent, ident)
         self.log.debug(str(completion_msg))
@@ -358,6 +360,7 @@ class Kernel(Configurable):
         else:
             hist = []
         content = {'history' : list(hist)}
+        content = json_clean(content)
         msg = self.session.send(self.shell_socket, 'history_reply',
                                 content, parent, ident)
         self.log.debug(str(msg))
@@ -409,7 +412,7 @@ class Kernel(Configurable):
         sys.stdout.flush()
 
         # Send the input request.
-        content = dict(prompt=prompt)
+        content = json_clean(dict(prompt=prompt))
         msg = self.session.send(self.stdin_socket, u'input_request', content, parent)
 
         # Await a response.
diff --git a/IPython/zmq/zmqshell.py b/IPython/zmq/zmqshell.py
index ac7df79..2bbf2a9 100644
--- a/IPython/zmq/zmqshell.py
+++ b/IPython/zmq/zmqshell.py
@@ -30,6 +30,7 @@ from IPython.core.macro import Macro
 from IPython.core.magic import MacroToEdit
 from IPython.core.payloadpage import install_payload_page
 from IPython.utils import io
+from IPython.utils.jsonutil import json_clean
 from IPython.utils.path import get_py_filename
 from IPython.utils.traitlets import Instance, Type, Dict, CBool
 from IPython.utils.warn import warn
@@ -69,7 +70,7 @@ class ZMQDisplayPublisher(DisplayPublisher):
         content['data'] = data
         content['metadata'] = metadata
         self.session.send(
-            self.pub_socket, u'display_data', content,
+            self.pub_socket, u'display_data', json_clean(content),
             parent=self.parent_header
         )
 
@@ -144,7 +145,7 @@ class ZMQInteractiveShell(InteractiveShell):
         dh = self.displayhook
         # Send exception info over pub socket for other clients than the caller
         # to pick up
-        exc_msg = dh.session.send(dh.pub_socket, u'pyerr', exc_content, dh.parent_header)
+        exc_msg = dh.session.send(dh.pub_socket, u'pyerr', json_clean(exc_content), dh.parent_header)
 
         # FIXME - Hack: store exception info in shell object.  Right now, the
         # caller is reading this info after the fact, we need to fix this logic