diff --git a/rollup/client.config.js b/rollup/client.config.js
index c81dfab..23c16cc 100644
--- a/rollup/client.config.js
+++ b/rollup/client.config.js
@@ -8,7 +8,7 @@ import config from 'sapper/config/rollup.js';
 
 const mode = process.env.NODE_ENV;
 const dev = mode === 'development';
-const legacy = process.env.SAPPER_LEGACY_BUILD;
+const legacy = !!process.env.SAPPER_LEGACY_BUILD;
 
 export default {
 	input: config.client.input(),