diff --git a/build-scripts/env.js b/build-scripts/env.js
index b12f20582f..e2eff4a4fa 100644
--- a/build-scripts/env.js
+++ b/build-scripts/env.js
@@ -27,7 +27,7 @@ module.exports = {
   version() {
     const version = fs
       .readFileSync(path.resolve(paths.polymer_dir, "pyproject.toml"), "utf8")
-      .match(/version\W+=\W"(\d{8}\.\d)"/);
+      .match(/version\W+=\W"(\d{8}\.\d(?:\.dev)?)"/);
     if (!version) {
       throw Error("Version not found");
     }