diff --git a/core/index.js b/core/index.js
index 9cdc22f..683f46c 100644
--- a/core/index.js
+++ b/core/index.js
@@ -18,7 +18,7 @@ async function core(options) {
 	// instantiate our data object, to be expanded upon
 	const data = {};
 
-	Object.keys(versions).map(async (version) => {
+	for (const version of Object.keys(versions)) {
 		// keep the pre-release identifiers, otherwise every Alpha release (like
 		// `v27.0.0-alpha.0.0.0`) would be coerced into `v27.0.0`
 		const versionSemver = semver.coerce(versions[version].version, {
@@ -133,10 +133,8 @@ async function core(options) {
 				data[name].support.phases.dates.end = schedule[name]?.end ?? undefined;
 			}
 			data[name].support.phases.current =
-				(await determineCurrentReleasePhase(
-					now,
-					data[name].support.phases.dates,
-				)) ?? {};
+				determineCurrentReleasePhase(now, data[name].support.phases.dates) ??
+				{};
 		}
 
 		// this is a slightly inefficient way to do this but it's also easy
@@ -194,12 +192,12 @@ async function core(options) {
 
 		data[name].releases[`v${versionSemver.version}`].security.isSecurity =
 			versions[version].security ?? false;
-	});
+	}
 
 	return data;
 }
 
-async function determineCurrentReleasePhase(now, dates = {}) {
+function determineCurrentReleasePhase(now, dates = {}) {
 	// we set set this up to enable custom `now` passing, since passing an ISO
 	// const usableNow = DateTime.fromISO(now)
 
diff --git a/core/test/errors.js b/core/test/errors.js
new file mode 100644
index 0000000..fca5c0a
--- /dev/null
+++ b/core/test/errors.js
@@ -0,0 +1,13 @@
+const { rejects } = require('node:assert');
+const nodevu = require('../index');
+const { describe, it } = require('node:test');
+
+describe('errors while building the data', async () => {
+	it('should reject when index.json has a version that cannot be parsed', async () => {
+		const index = [{ version: 'not-a-version', files: [] }];
+		const fetch = async (url) =>
+			Response.json(url.endsWith('schedule.json') ? {} : index);
+
+		await rejects(nodevu({ fetch, now: '2024-01-01T00:00:00.000Z' }));
+	});
+});