diff --git a/pre_commit_hooks/util.py b/pre_commit_hooks/util.py
index eedf7b6..7c2175e 100644
--- a/pre_commit_hooks/util.py
+++ b/pre_commit_hooks/util.py
@@ -2,10 +2,26 @@
 from __future__ import print_function
 from __future__ import unicode_literals
 
-from plumbum import local
+import subprocess
+
+
+class CalledProcessError(RuntimeError):
+    pass
 
 
 def added_files():
-    return set(local['git'](
-        'diff', '--staged', '--name-only', '--diff-filter', 'A',
+    return set(cmd_output(
+        'git', 'diff', '--staged', '--name-only', '--diff-filter', 'A',
     ).splitlines())
+
+
+def cmd_output(*cmd, **kwargs):
+    retcode = kwargs.pop('retcode', 0)
+    popen_kwargs = {'stdout': subprocess.PIPE, 'stderr': subprocess.PIPE}
+    popen_kwargs.update(kwargs)
+    proc = subprocess.Popen(cmd, **popen_kwargs)
+    stdout, stderr = proc.communicate()
+    stdout, stderr = stdout.decode('UTF-8'), stderr.decode('UTF-8')
+    if retcode is not None and proc.returncode != retcode:
+        raise CalledProcessError(cmd, retcode, proc.returncode, stdout, stderr)
+    return stdout