diff --git a/utils/arcanist/clang-format.sh b/utils/arcanist/clang-format.sh
--- a/utils/arcanist/clang-format.sh
+++ b/utils/arcanist/clang-format.sh
@@ -4,17 +4,23 @@
 
 # "script-and-regex.regex": "/^(?P<severity>.*?)\n(?P<message>.*?)\n(?P<line>\\d),(?P<char>\\d)(\n(?P<original>.*?)>>>>\n(?P<replacement>.*?)<<<<?)$/s",
 
-# Arcanist linter that invokes clang-format.
+# Arcanist linter that invokes clang-format via clang/tools/clang-format/clang-format-diff.py
 # stdout from this script is parsed into a regex and used by Arcanist.
 # https://secure.phabricator.com/book/phabricator/article/arcanist_lint_script_and_regex/
 
 # To skip running all linters when creating/updating a diff, use `arc diff --nolint`.
 
-if ! hash clang-format-diff >/dev/null; then
-  # advice severity level is completely non-disruptive.
-  # switch to warning or error if you want to prompt the user.
+# advice severity level is completely non-disruptive.
+# switch to warning or error if you want to prompt the user.
+if ! hash clang-format >/dev/null; then
   echo "advice"
-  echo "clang-format-diff not found in user's PATH; not linting file."
+  echo "clang-format not found in user's PATH; not linting file."
+  echo "===="
+  exit 0
+fi
+if ! git rev-parse --git-dir >/dev/null; then
+  echo "advice"
+  echo "not in git repostitory; not linting file."
   echo "===="
   exit 0
 fi
@@ -37,14 +43,17 @@
 
 # Arcanist can filter out lint messages for unchanged lines, but for that, we
 # need to generate line by line lint messages. Instead, we generate one lint
-# message on line 1, char 1 with file content edited using clang-format-diff.
-if git rev-parse --git-dir >/dev/null; then
-  arc_base_commit=$(arc which --show-base)
-  # An alternative is to use git-clang-format.
-  git diff -U0 --no-color "${arc_base_commit}"| clang-format-diff -style file -i -p1
-else
-  svn diff --diff-cmd=diff -x -U0 "${src_file}" | clang-format-diff -style LLVM -i
-fi
+# message on line 1, char 1 with file content edited using clang-format-diff.py
+#
+# We do not use git-clang-format because it wants to modify the index,
+# and arc is already holding the lock.
+#
+# We do not look for clang-format-diff or clang-format-diff.py in the PATH
+# because whether/how these are installed differs between distributions,
+# and we have an executable copy in the tree anyway.
+arc_base_commit=$(arc which --show-base)
+git diff -U0 --no-color "${arc_base_commit}" \
+  | clang/tools/clang-format/clang-format-diff.py -style file -i -p1
 
 cp -p "${src_file}" "${formatted_file}"
 cp -p "${original_file}" "${src_file}"