diff --git a/cpplint/cpplint.py b/cpplint/cpplint.py
index 0445454..159dbbb 100755
--- a/cpplint/cpplint.py
+++ b/cpplint/cpplint.py
@@ -136,6 +136,22 @@
       the top-level categories like 'build' and 'whitespace' will
       also be printed. If 'detailed' is provided, then a count
       is provided for each category like 'build/class'.
+
+    root=subdir
+      The root directory used for deriving header guard CPP variable.
+      By default, the header guard CPP variable is calculated as the relative
+      path to the directory that contains .git, .hg, or .svn.  When this flag
+      is specified, the relative path is calculated from the specified
+      directory. If the specified directory does not exist, this flag is
+      ignored.
+
+      Examples:
+        Assuing that src/.git exists, the header guard CPP variables for
+        src/chrome/browser/ui/browser.h are:
+
+        No flag => CHROME_BROWSER_UI_BROWSER_H_
+        --root=chrome => BROWSER_UI_BROWSER_H_
+        --root=chrome/browser => UI_BROWSER_H_
 """
 
 # We categorize each error message we print.  Here are the categories.
@@ -336,6 +352,10 @@
 # on which those errors are expected and should be suppressed.
 _error_suppressions = {}
 
+# The root directory used for deriving header guard CPP variable.
+# This is set by --root flag.
+_root = None
+
 def ParseNolintSuppressions(filename, raw_line, linenum, error):
   """Updates the global list of error-suppressions.
 
@@ -1102,7 +1122,10 @@
   filename = re.sub(r'/\.flymake/([^/]*)$', r'/\1', filename)
 
   fileinfo = FileInfo(filename)
-  return re.sub(r'[-./\s]', '_', fileinfo.RepositoryName()).upper() + '_'
+  file_path_from_root = fileinfo.RepositoryName()
+  if _root:
+    file_path_from_root = re.sub('^' + _root + os.sep, '', file_path_from_root)
+  return re.sub(r'[-./\s]', '_', file_path_from_root).upper() + '_'
 
 
 def CheckForHeaderGuard(filename, lines, error):
@@ -3933,7 +3956,8 @@
   try:
     (opts, filenames) = getopt.getopt(args, '', ['help', 'output=', 'verbose=',
                                                  'counting=',
-                                                 'filter='])
+                                                 'filter=',
+                                                 'root='])
   except getopt.GetoptError:
     PrintUsage('Invalid arguments.')
 
@@ -3959,6 +3983,9 @@
       if val not in ('total', 'toplevel', 'detailed'):
         PrintUsage('Valid counting options are total, toplevel, and detailed')
       counting_style = val
+    elif opt == '--root':
+      global _root
+      _root = val
 
   if not filenames:
     PrintUsage('No files were specified.')