Index: google3/third_party/llvm/llvm/tools/clang/tools/clang-format/git-clang-format
===================================================================
--- google3/third_party/llvm/llvm/tools/clang/tools/clang-format/git-clang-format
+++ google3/third_party/llvm/llvm/tools/clang/tools/clang-format/git-clang-format
@@ -153,7 +153,7 @@
   # those files.
   cd_to_toplevel()
   if len(commits) > 1:
-    old_tree = commits[1]
+    old_tree = commits[0]
     new_tree = run_clang_format_and_save_to_tree(changed_lines,
                                                  revision=commits[1],
                                                  binary=opts.binary,