diff --git a/npm_scripts/cleancss.js b/npm_scripts/cleancss.js
index 3b774028a..036cefade 100755
--- a/npm_scripts/cleancss.js
+++ b/npm_scripts/cleancss.js
@@ -57,7 +57,7 @@ function cleanCss(inputDir, outputDir) {
     // set the rebase path, this is required otherwise the source map file is not found
     cleanCssOptions.rebaseTo = outputDir;
     ensureDir(cleanCssOptions.rebaseTo);
-    const files = globSync(inputDir);
+    const files = globSync( (process.platform === "win32") ?  inputDir.replace(/\\/g, '/') : inputDir);
     for (var i = 0; i < files.length; i++) {
         var f = files[i];
         var o = path.normalize(outputDir + '/' + path.basename(f, '.css') + '.min.css');
@@ -97,4 +97,4 @@ if (argv.cleancss) {
         cleanCssOptions.sourceMapInlineSources=false;
     }
     cleanCss(argv.inputDir, argv.outputDir);
-}
\ No newline at end of file
+}