diff --git a/lib/BannerPlugin.js b/lib/BannerPlugin.js
index 80c66a5ac..cdef1ab9b 100644
--- a/lib/BannerPlugin.js
+++ b/lib/BannerPlugin.js
@@ -38,7 +38,7 @@ class BannerPlugin {
 
 		validateOptions(schema, options, "Banner Plugin");
 
-		if (typeof options === "string" || typeof options === "function") {
+		if (["string", "function"].indexOf(typeof options) !== -1) {
 			options = {
 				banner: options
 			};