diff --git a/README.md b/README.md
index 7ec5de2..078eed8 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ While you can install `packwatch` as a global package, it's better to include it
 
 ## Usage
 
-`packwatch` tracks your packages' size via its `.packwatch.json` manifest. To get started, call `packwatch` at the root of your project: a fresh manifest will be generated for you using your current package's size as the initial upper limit for package size.
+`packwatch` tracks your packages' size via its `.packwatch.json` manifest. To get started, call `packwatch --update-manifest` at the root of your project: a fresh manifest will be generated for you using your current package's size as the initial upper limit for package size.
 
 Once a manifest file exists, calling `packwatch` again will compare its data to the current state of your package. Every time `packwatch` compares your code to the manifest, it will update the last reported package size statistics it contains, but not the limit you have set.
 
diff --git a/src/index.js b/src/index.js
index d3f3f23..cf69e65 100644
--- a/src/index.js
+++ b/src/index.js
@@ -16,7 +16,9 @@ if (!existsSync('package.json')) {
     process.exit(1)
 }
 
-const isUpdatingManifest = process.argv.includes('--update-manifest')
+const UPDATE_MANIFEST_OPTION = '--update-manifest'
+
+const isUpdatingManifest = process.argv.includes(UPDATE_MANIFEST_OPTION)
 
 const currentStats = getCurrentPackageStats()
 
@@ -26,6 +28,13 @@ const currentStats = getCurrentPackageStats()
  */
 
 if (!existsSync(MANIFEST_FILENAME)) {
+    if (!isUpdatingManifest) {
+        console.log(
+            `🔥🔥📦🔥🔥 No manifest file exists! Run packwatch with ${UPDATE_MANIFEST_OPTION} to generate a manifest file`,
+        )
+        process.exit(1)
+    }
+
     createOrUpdateManifest({ current: currentStats })
     console.log(
         `📝 No Manifest to compare against! Current package stats written to ${MANIFEST_FILENAME}!`,