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
@@ -41,6 +41,7 @@
 
 import difflib
 import json
+import os.path
 import platform
 import subprocess
 import sys
@@ -76,7 +77,8 @@
   # 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)