diff --git a/clang/tools/clang-format/clang-format.py b/clang/tools/clang-format/clang-format.py
--- a/clang/tools/clang-format/clang-format.py
+++ b/clang/tools/clang-format/clang-format.py
@@ -45,6 +45,7 @@
 import subprocess
 import sys
 import vim
+import os.path
 
 # set g:clang_format_path to the path to clang-format if it is not on the path
 # Change this to the full path if clang-format is not on the path.
@@ -76,7 +77,7 @@
   # Determine range to format.
   if vim.eval('exists("l:lines")') == '1':
     lines = ['-lines', vim.eval('l:lines')]
-  elif vim.eval('exists("l:formatdiff")') == '1':
+  elif vim.eval('exists("l:formatdiff")') == '1' and os.path.exists(vim.current.buffer.name):
     with open(vim.current.buffer.name, 'r') as f:
       ondisk = f.read().splitlines();
     sequence = difflib.SequenceMatcher(None, ondisk, vim.current.buffer)