diff --git a/src/__tests__/index.test.ts b/src/__tests__/index.test.ts
index e44cd52..f9cacdf 100644
--- a/src/__tests__/index.test.ts
+++ b/src/__tests__/index.test.ts
@@ -53,7 +53,9 @@ describe('Packwatch', () => {
 
     it('warns the user and errors if run away from package.json', async () => {
         workspacePath = await prepareWorkspace()
-        await packwatch({ cwd: workspacePath })
+        await expect(async () =>
+            packwatch({ cwd: workspacePath }),
+        ).rejects.toThrow('NOT_IN_PACKAGE_ROOT')
 
         expect(mockLogger.mock.calls).toHaveLength(1)
         expect(mockLogger.mock.calls[0][0]).toEqual(
diff --git a/src/index.ts b/src/index.ts
index a41a650..f464536 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -7,6 +7,7 @@ import {
     getPreviousPackageStats,
 } from './utils'
 import type { PackwatchArguments } from './index.d'
+import { assertInPackageRoot } from './invariants'
 
 const MANIFEST_FILENAME = '.packwatch.json'
 
@@ -14,15 +15,9 @@ export default async function packwatch({
     cwd,
     isUpdatingManifest,
 }: PackwatchArguments): Promise<void> {
-    const packageJsonPath = resolve(join(cwd, 'package.json'))
     const manifestPath = resolve(join(cwd, MANIFEST_FILENAME))
 
-    if (!existsSync(packageJsonPath)) {
-        console.log(
-            '🤔 There is no package.json file here. Are you in the root directory of your project?',
-        )
-        return
-    }
+    assertInPackageRoot(cwd)
 
     const currentStats = getCurrentPackageStats(cwd)
 
diff --git a/src/invariants.ts b/src/invariants.ts
new file mode 100644
index 0000000..ed8839e
--- /dev/null
+++ b/src/invariants.ts
@@ -0,0 +1,14 @@
+import { existsSync } from 'fs'
+import { join, resolve } from 'path'
+
+export function assertInPackageRoot(cwd: string): void {
+    const packagePath = resolve(join(cwd, 'package.json'))
+    const packageJsonExists = existsSync(packagePath)
+
+    if (!packageJsonExists) {
+        console.log(
+            '🤔 There is no package.json file here. Are you in the root directory of your project?',
+        )
+        throw new Error('NOT_IN_PACKAGE_ROOT')
+    }
+}