diff --git a/lib/BannerPlugin.js b/lib/BannerPlugin.js
index 1163617875a..d3a3afb187e 100644
--- a/lib/BannerPlugin.js
+++ b/lib/BannerPlugin.js
@@ -47,10 +47,12 @@ class BannerPlugin {
 								filename = filename.substr(0, querySplit);
 							}
 
-							if(filename.indexOf("/") < 0) {
+							const lastSlashIndex = filename.lastIndexOf("/");
+
+							if(lastSlashIndex === -1) {
 								basename = filename;
 							} else {
-								basename = filename.substr(filename.lastIndexOf("/") + 1);
+								basename = filename.substr(lastSlashIndex + 1);
 							}
 
 							const comment = compilation.getPath(banner, {