--- a/python/mozlint/mozlint/cli.py
+++ b/python/mozlint/mozlint/cli.py
@@ -57,58 +57,70 @@ class MozlintParser(ArgumentParser):
 
     def __init__(self, **kwargs):
         ArgumentParser.__init__(self, usage=self.__doc__, **kwargs)
 
         for cli, args in self.arguments:
             self.add_argument(*cli, **args)
 
 
-class VCFiles(object):
+class VCSFiles(object):
     def __init__(self):
+        self._root = None
         self._vcs = None
 
     @property
+    def root(self):
+        if self._root:
+            return self._root
+
+        # First check if we're in an hg repo, if not try git
+        commands = (
+            ['hg', 'root'],
+            ['git', 'rev-parse', '--show-toplevel'],
+        )
+
+        for cmd in commands:
+            proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
+            output = proc.communicate()[0].strip()
+
+            if proc.returncode == 0:
+                self._vcs = cmd[0]
+                self._root = output
+                return self._root
+
+    @property
     def vcs(self):
-        if self._vcs:
-            return self._vcs
-
-        self._vcs = 'none'
-        with open(os.devnull, 'wb') as DEVNULL:
-            if not subprocess.call(['hg', 'root'], stdout=DEVNULL):
-                self._vcs = 'hg'
-            elif not subprocess.call(['git', 'rev-parse'], stdout=DEVNULL):
-                self._vcs = 'git'
-        return self._vcs
+        return self._vcs or (self.root and self._vcs)
 
     @property
     def is_hg(self):
         return self.vcs == 'hg'
 
     @property
     def is_git(self):
         return self.vcs == 'git'
 
+    def _run(self, cmd):
+        files = subprocess.check_output(cmd).split()
+        return [os.path.join(self.root, f) for f in files]
+
     def by_rev(self, rev):
         if self.is_hg:
-            cmd = ['hg', 'log', '-T', '{files % "\\n{file}"}', '-r', rev]
-        elif self.is_git(self):
-            cmd = ['git', 'diff', '--name-only', rev]
-        else:
-            return []
-        return subprocess.check_output(cmd).split()
+            return self._run(['hg', 'log', '-T', '{files % "\\n{file}"}', '-r', rev])
+        elif self.is_git:
+            return self._run(['git', 'diff', '--name-only', rev])
+        return []
 
     def by_workdir(self):
         if self.is_hg:
-            cmd = ['hg', 'status', '-amn']
-        elif self.is_git(self):
-            cmd = ['git', 'diff', '--name-only']
-        else:
-            return []
-        return subprocess.check_output(cmd).split()
+            return self._run(['hg', 'status', '-amn'])
+        elif self.is_git:
+            return self._run(['git', 'diff', '--name-only'])
+        return []
 
 
 def find_linters(linters=None):
     lints = []
     for search_path in SEARCH_PATHS:
         if not os.path.isdir(search_path):
             continue
 
@@ -124,21 +136,21 @@ def find_linters(linters=None):
             lints.append(os.path.join(search_path, f))
     return lints
 
 
 def run(paths, linters, fmt, rev, workdir, **lintargs):
     from mozlint import LintRoller, formatters
 
     # Calculate files from VCS
-    vcfiles = VCFiles()
+    vcs = VCSFiles()
     if rev:
-        paths.extend(vcfiles.by_rev(rev))
+        paths.extend(vcs.by_rev(rev))
     if workdir:
-        paths.extend(vcfiles.by_workdir())
+        paths.extend(vcs.by_workdir())
     paths = paths or ['.']
 
     lint = LintRoller(**lintargs)
     lint.read(find_linters(linters))
 
     # run all linters
     results = lint.roll(paths)