diff --git a/Makefile b/Makefile
index 61e980d..997f47e 100644
--- a/Makefile
+++ b/Makefile
@@ -63,6 +63,10 @@ testpypi: clean sdist bdist_wheel
 pypi: clean sdist bdist_wheel
 	twine upload dist/*
 
+.PHONY: on_master
+on_master:
+	./on_master.sh
+
 .PHONY: tag
-tag:
+tag: on_master
 	git tag -a $$(python -c 'from flake8_aaa.__about__ import __version__; print("v{}".format(__version__))')
diff --git a/on_master.sh b/on_master.sh
new file mode 100755
index 0000000..855374c
--- /dev/null
+++ b/on_master.sh
@@ -0,0 +1,12 @@
+#!/bin/bash
+
+set -eo pipefail
+
+git fetch origin -v
+
+branch_info=$(git status --short -b | head -1)
+
+if [[ $branch_info != '## master...origin/master' ]]; then
+    echo "Not on master or master not up to date with origin, branch = $branch_info"
+    exit 1
+fi