diff --git a/pre_commit/xargs.py b/pre_commit/xargs.py
index eea3acdb..1b237a38 100644
--- a/pre_commit/xargs.py
+++ b/pre_commit/xargs.py
@@ -1,41 +1,54 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 
+import sys
+
 from pre_commit import parse_shebang
 from pre_commit.util import cmd_output
 
 
-# Limit used previously to avoid "xargs ... Bad file number" on windows
-# This is slightly less than the posix mandated minimum
-MAX_LENGTH = 4000
+# TODO: properly compute max_length value
+def _get_platform_max_length():
+    # posix minimum
+    return 4 * 1024
+
+
+def _get_command_length(command, arg):
+    parts = command + (arg,)
+    full_cmd = ' '.join(parts)
+
+    # win32 uses the amount of characters, more details at:
+    # https://blogs.msdn.microsoft.com/oldnewthing/20031210-00/?p=41553/
+    if sys.platform == 'win32':
+        return len(full_cmd)
+
+    return len(full_cmd.encode(sys.getdefaultencoding()))
 
 
 class ArgumentTooLongError(RuntimeError):
     pass
 
 
-def partition(cmd, varargs, _max_length=MAX_LENGTH):
+def partition(cmd, varargs, _max_length=None):
+    _max_length = _max_length or _get_platform_max_length()
     cmd = tuple(cmd)
     ret = []
 
     ret_cmd = []
-    total_len = len(' '.join(cmd))
     # Reversed so arguments are in order
     varargs = list(reversed(varargs))
 
     while varargs:
         arg = varargs.pop()
 
-        if total_len + 1 + len(arg) <= _max_length:
+        if _get_command_length(cmd + tuple(ret_cmd), arg) <= _max_length:
             ret_cmd.append(arg)
-            total_len += len(arg)
         elif not ret_cmd:
             raise ArgumentTooLongError(arg)
         else:
             # We've exceeded the length, yield a command
             ret.append(cmd + tuple(ret_cmd))
             ret_cmd = []
-            total_len = len(' '.join(cmd))
             varargs.append(arg)
 
     ret.append(cmd + tuple(ret_cmd))
diff --git a/tests/xargs_test.py b/tests/xargs_test.py
index 529eb197..84d4899b 100644
--- a/tests/xargs_test.py
+++ b/tests/xargs_test.py
@@ -1,11 +1,29 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 
+from unittest import mock
+
 import pytest
 
 from pre_commit import xargs
 
 
+@pytest.fixture
+def sys_win32_mock():
+    return mock.Mock(
+        platform='win32',
+        getdefaultencoding=mock.Mock(return_value='utf-8'),
+    )
+
+
+@pytest.fixture
+def sys_linux_mock():
+    return mock.Mock(
+        platform='linux',
+        getdefaultencoding=mock.Mock(return_value='utf-8'),
+    )
+
+
 def test_partition_trivial():
     assert xargs.partition(('cmd',), ()) == (('cmd',),)
 
@@ -35,6 +53,32 @@ def test_partition_limits():
     )
 
 
+def test_partition_limit_win32(sys_win32_mock):
+    cmd = ('ninechars',)
+    varargs = ('😑' * 10,)
+    with mock.patch('pre_commit.xargs.sys', sys_win32_mock):
+        ret = xargs.partition(cmd, varargs, _max_length=20)
+
+    assert ret == (cmd + varargs,)
+
+
+def test_partition_limit_linux(sys_linux_mock):
+    cmd = ('ninechars',)
+    varargs = ('😑' * 5,)
+    with mock.patch('pre_commit.xargs.sys', sys_linux_mock):
+        ret = xargs.partition(cmd, varargs, _max_length=30)
+
+    assert ret == (cmd + varargs,)
+
+
+def test_argument_too_long_with_large_unicode(sys_linux_mock):
+    cmd = ('ninechars',)
+    varargs = ('😑' * 10,)  # 4 bytes * 10
+    with mock.patch('pre_commit.xargs.sys', sys_linux_mock):
+        with pytest.raises(xargs.ArgumentTooLongError):
+            xargs.partition(cmd, varargs, _max_length=20)
+
+
 def test_argument_too_long():
     with pytest.raises(xargs.ArgumentTooLongError):
         xargs.partition(('a' * 5,), ('a' * 5,), _max_length=10)