diff --git a/README.md b/README.md
index 4f0a8ea7..8756be18 100644
--- a/README.md
+++ b/README.md
@@ -158,7 +158,7 @@ Options
 	-v, --version    Displays current version
 	-i, --entry      Entry module(s)
 	-o, --output     Directory to place build files into
-	-f, --format     Only build specified formats  (default modern,es,cjs,umd)
+	-f, --format     Only build specified formats (any of modern,es,cjs,umd or iife) (default modern,es,cjs,umd)
 	-w, --watch      Rebuilds on any change  (default false)
 	--target         Specify your target environment (node or web)  (default web)
 	--external       Specify external dependencies, or 'none'
diff --git a/src/prog.js b/src/prog.js
index 9029b60e..c47bae9a 100644
--- a/src/prog.js
+++ b/src/prog.js
@@ -22,7 +22,11 @@ export default handler => {
 		.version(version)
 		.option('--entry, -i', 'Entry module(s)')
 		.option('--output, -o', 'Directory to place build files into')
-		.option('--format, -f', 'Only build specified formats', DEFAULT_FORMATS)
+		.option(
+			'--format, -f',
+			`Only build specified formats (any of ${DEFAULT_FORMATS} or iife)`,
+			DEFAULT_FORMATS,
+		)
 		.option('--watch, -w', 'Rebuilds on any change', false)
 		.option('--target', 'Specify your target environment (node or web)', 'web')
 		.option('--external', `Specify external dependencies, or 'none'`)