diff --git a/is-clean.sh b/is-clean.sh
index 83956e5c9..b63b54f46 100755
--- a/is-clean.sh
+++ b/is-clean.sh
@@ -1,6 +1,21 @@
 #!/usr/bin/env bash
 
-if ! ( output=$(git status --porcelain) && [ -z "$output" ] ); then
+set -e
+
+if [ -n "$(git status --porcelain)" ]; then
     echo "Working directory isn't clean" >&2
     exit 1
 fi
+
+if [ "$(git rev-parse --abbrev-ref HEAD)" != "master" ]; then
+    echo "Not on master" >&2
+    exit 1
+fi
+
+ourHash=$(git rev-parse HEAD)
+theirHash=$(git ls-remote origin -h refs/heads/master | awk '{ print $1; }')
+
+if [ "$theirHash" != "$ourHash" ]; then
+    echo "Local HEAD is not up to date with remote master" >&2
+    exit 1
+fi