diff --git a/src/lib/determine-as-value.js b/src/lib/determine-as-value.js
index 7652599..3bf221b 100644
--- a/src/lib/determine-as-value.js
+++ b/src/lib/determine-as-value.js
@@ -36,7 +36,7 @@ function determineAsValue ({ optionsAs, href }) {
       // value based on the suffix of filename.
 
       // We only care about the pathname, so just use any domain when constructing the URL.
-      const url = new URL(href, 'https://example.com')
+      const url = new URL(href, 'https://example.com/')
       const extension = path.extname(url.pathname)
 
       if (extension === '.css') {