diff --git a/tools/clang_util.py b/tools/clang_util.py
index 3b8e8b422..b0e81396c 100644
--- a/tools/clang_util.py
+++ b/tools/clang_util.py
@@ -3,16 +3,26 @@
 # can be found in the LICENSE file
 
 from exec_util import exec_cmd
+import os
 import sys
 
+# Script directory.
+script_dir = os.path.dirname(__file__)
+root_dir = os.path.join(script_dir, os.pardir)
+
 if sys.platform == 'win32':
   # Force use of the clang-format version bundled with depot_tools.
   clang_format_exe = 'clang-format.bat'
 else:
   clang_format_exe = 'clang-format'
 
-def clang_format(file_contents):
-  result = exec_cmd(clang_format_exe, ".", file_contents)
+def clang_format(file_name, file_contents):
+  # -assume-filename is necessary to find the .clang-format file and determine
+  # the language when specifying contents via stdin.
+  result = exec_cmd("%s -assume-filename=%s" % (clang_format_exe, file_name), \
+                    root_dir, file_contents)
+  if result['err'] != '':
+    print "clang-format error: %s" % result['err']
   if result['out'] != '':
     output = result['out']
     if sys.platform == 'win32':
diff --git a/tools/fix_style.py b/tools/fix_style.py
index e65dbeb6d..1456cafc7 100644
--- a/tools/fix_style.py
+++ b/tools/fix_style.py
@@ -34,7 +34,7 @@ def update_file(filename):
     msg(filename, "empty")
     return;
 
-  newcontents = clang_format(oldcontents)
+  newcontents = clang_format(filename, oldcontents)
   if newcontents is None:
     raise Exception("Failed to process %s" % filename)
 
diff --git a/tools/translator.py b/tools/translator.py
index 0b07f160f..277fc3f7e 100644
--- a/tools/translator.py
+++ b/tools/translator.py
@@ -124,7 +124,7 @@ def update_file(file, newcontents):
 
     # Apply clang-format for C/C++ files.
     if os.path.splitext(file)[1][1:] in ('cc', 'cpp', 'h'):
-        result = clang_format(newcontents)
+        result = clang_format(file, newcontents)
         if result != None:
             newcontents = result
         else: