diff --git a/rollup.config.js b/rollup.config.js
index de027ad7702b..f70338cd9337 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -190,7 +190,7 @@ export function makeBaseBundleConfig(options) {
       esModule: false,
     },
     plugins: [
-      jsVersion === 'es5' ? typescriptPluginES5 : typescriptPluginES6,
+      jsVersion.toLowerCase() === 'es5' ? typescriptPluginES5 : typescriptPluginES6,
       markAsBrowserBuildPlugin,
       nodeResolvePlugin,
       licensePlugin,