diff --git a/procrunner/__init__.py b/procrunner/__init__.py
index 711b4b6..896f599 100644
--- a/procrunner/__init__.py
+++ b/procrunner/__init__.py
@@ -2,6 +2,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+import codecs
 import copy
 import logging
 import os
@@ -67,12 +68,14 @@
     self._buffer = ''
     self._print = print_line
     self._callback = callback
+    self._decoder = codecs.getincrementaldecoder('utf-8')('replace')
   def add(self, data):
     '''Add a single character to buffer. If one or more full lines are found,
        print them (if desired) and pass to callback function.'''
-    data = data.decode('utf-8')
+    data = self._decoder.decode(data)
+    if not data: return
     self._buffer += data
-    if "\n" in data:
+    if '\n' in data:
       to_print, remainder = self._buffer.rsplit('\n')
       if self._print:
         print(to_print)
@@ -81,6 +84,7 @@
       self._buffer = remainder
   def flush(self):
     '''Print/send any remaining data to callback function.'''
+    self._buffer += self._decoder.decode(b'', final=True)
     if self._buffer:
       if self._print:
         print(self._buffer)
diff --git a/tests/test_procrunner_system.py b/tests/test_procrunner_system.py
index 174a52f..ba1b7ea 100644
--- a/tests/test_procrunner_system.py
+++ b/tests/test_procrunner_system.py
@@ -4,6 +4,7 @@
 import sys
 
 import procrunner
+import pytest
 
 def test_simple_command_invocation():
   if os.name == 'nt':
@@ -17,10 +18,27 @@
   assert result['stdout'] == b'hello' + os.linesep.encode('utf-8')
   assert result['stderr'] == b''
 
-def test_input_encoding():
+def test_decode_invalid_utf8_input(capsys):
   command = [sys.executable, '-c', 'import sys; sys.stdout.write("".join(chr(x) for x in '
-             '(0x74,0x65,0x73,0x74,0xa0,0x50,0x73,0x74,0x72,0x69,0x6e,0x67,0x0a)'
+             '(0x74,0x65,0x73,0x74,0xa0,0x73,0x74,0x72,0x69,0x6e,0x67,0x0a)'
              '))']
   result = procrunner.run(command)
+  assert result['exitcode'] == 0
+  assert not result['stderr']
+  assert result['stdout'] == b'test\xa0string\n'
+  out, err = capsys.readouterr()
+  assert out == u'test\ufffdstring\n'
+  assert err == u''
 
+def test_running_wget(tmpdir):
+  tmpdir.chdir()
+  command = ['wget', 'https://www.google.com', '-O', '-']
+  try:
+    result = procrunner.run(command)
+  except OSError as e:
+    if e.errno == 2:
+      pytest.skip('wget not available')
+    raise
   assert result['exitcode'] == 0
+  assert b'http' in result['stderr']
+  assert b'google' in result['stdout']