diff --git a/preupload-hooks/GLOBAL-PREUPLOAD.cfg b/preupload-hooks/GLOBAL-PREUPLOAD.cfg
index b87fdec..1ae4480 100644
--- a/preupload-hooks/GLOBAL-PREUPLOAD.cfg
+++ b/preupload-hooks/GLOBAL-PREUPLOAD.cfg
@@ -11,3 +11,8 @@
 
 [Builtin Hooks Options]
 clang_format = --commit ${PREUPLOAD_COMMIT} --style file --extensions c,h,cc,cpp
+
+[Hook Scripts]
+yapf-diff = ${REPO_ROOT}/scripts/preupload-hooks/yapf-diff.sh ${PREUPLOAD_COMMIT}
+# Add the following line to a project-local config file to bypass yapf-diff:
+# yapf-diff = ${REPO_ROOT}/scripts/preupload-hooks/yapf-diff.sh --bypass
diff --git a/preupload-hooks/yapf-diff.sh b/preupload-hooks/yapf-diff.sh
new file mode 100755
index 0000000..a0d22bf
--- /dev/null
+++ b/preupload-hooks/yapf-diff.sh
@@ -0,0 +1,30 @@
+#! /bin/bash
+# Wrapper to run yapf-diff for repo preupload.
+# Usage: if the first argument is --bypass, do nothing (exit 0). If the first
+# argument is a git hash, run yapf-diff on that commit, otherwise run yapf-diff
+# on the last commit. Any other arguments are passed to yapf-diff.
+# The script fails if yapf-diff produces any output.
+
+COMMIT="$(git log --format='%H' -1)"
+
+if [ $# -gt 0 ] ; then
+    if [ "$1" == "--bypass" ] ; then
+        exit 0
+    fi
+
+    if [[ ! "$1" =~ ^- ]] ; then
+        COMMIT="$1"
+        shift
+    fi
+fi
+
+if git show -U0 --no-color "${COMMIT}" | yapf-diff "$@" | grep --color=never . ; then
+    cat <<EOF
+
+
+Please fix the formatting issues above before uploading.
+You can apply the changes above by running:
+$0 $COMMIT -i
+EOF
+    exit 1
+fi
diff --git a/python-requirements.txt b/python-requirements.txt
index b8e0d81..24e6f1c 100644
--- a/python-requirements.txt
+++ b/python-requirements.txt
@@ -19,3 +19,4 @@
 setuptools
 tempita
 wget
+yapf