diff --git a/is-clean.sh b/is-clean.sh
new file mode 100755
index 000000000..83956e5c9
--- /dev/null
+++ b/is-clean.sh
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+if ! ( output=$(git status --porcelain) && [ -z "$output" ] ); then
+    echo "Working directory isn't clean" >&2
+    exit 1
+fi
diff --git a/package.json b/package.json
index 4a1187eba..54278208b 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,7 @@
     "frontend:test:watch": "karma start --conf karma.conf.js --single-run false",
     "frontend:build": "webpack",
     "frontend:build:watch": "webpack --watch",
-    "prerelease": "npm run test",
+    "prerelease": "./is-clean.sh && npm run test",
     "release": "standard-version -a",
     "postrelease": "git push --follow-tags origin master"
   },