diff --git a/lib/datasource/packagist.js b/lib/datasource/packagist.js
index 7488f5e8e874721868ce12dd813792754fe5a245..c2c2e3423a2856ed864bbc84e2bbb17fbaec6d31 100644
--- a/lib/datasource/packagist.js
+++ b/lib/datasource/packagist.js
@@ -23,7 +23,8 @@ function authGot(url) {
 
 async function getRegistryMeta(regUrl) {
   try {
-    const res = (await authGot(regUrl + '/packages.json')).body;
+    const url = URL.resolve(regUrl, 'packages.json');
+    const res = (await authGot(url)).body;
     const meta = {};
     meta.packages = res.packages;
     if (res.includes) {