diff --git a/src/index.js b/src/index.js
index 2f0f849..1092f51 100644
--- a/src/index.js
+++ b/src/index.js
@@ -46,7 +46,6 @@ async function run(octokit, context, token) {
 		stripHash: stripHash(getInput('strip-hash'))
 	});
 
-	const buildScript = getInput('build-script') || 'build';
 	const cwd = process.cwd();
 
 	let { packageManager, installScript } = await getPackageManagerAndInstallScript(cwd);
@@ -54,14 +53,16 @@ async function run(octokit, context, token) {
 		installScript = getInput('install-script');
 	}
 
+	const buildScript = getInput('build-script') || `${packageManager} run build`;
+
 	startGroup(`[current] Install Dependencies`);
 	console.log(`Installing using ${installScript}`);
 	await exec(installScript);
 	endGroup();
 
 	startGroup(`[current] Build using ${packageManager}`);
-	console.log(`Building using ${packageManager} run ${buildScript}`);
-	await exec(`${packageManager} run ${buildScript}`);
+	console.log(`Building using ${buildScript}`);
+	await exec(buildScript);
 	endGroup();
 
 	// In case the build step alters a JSON-file, ....
@@ -69,9 +70,19 @@ async function run(octokit, context, token) {
 
 	const newSizes = await plugin.readFromDisk(cwd);
 
+	function throwIfBaseRefMissing() {
+		if (!baseRef) {
+			if (context.eventName == 'push') {
+				throw new Error('missing context.payload.base.ref for push event');
+			} else {
+				throw new Error('missing context.payload.pull_request.base.ref for pull_request event');
+			}
+		}
+	}
+
 	startGroup(`[base] Checkout target branch`);
 	try {
-		if (!baseRef) throw Error('missing context.payload.pull_request.base.ref');
+		throwIfBaseRefMissing();
 		await exec(`git fetch -n origin ${baseRef}:${baseRef}`);
 		console.log('successfully fetched base.ref');
 	} catch (e) {
@@ -98,7 +109,7 @@ async function run(octokit, context, token) {
 
 	console.log('checking out and building base commit');
 	try {
-		if (!baseRef) throw Error('missing context.payload.base.ref');
+		throwIfBaseRefMissing();
 		await exec(`git reset --hard ${baseRef}`);
 	} catch (e) {
 		await exec(`git reset --hard ${baseSha}`);