diff --git a/lib/modules/manager/sbt/extract.ts b/lib/modules/manager/sbt/extract.ts
index 2009306a2f92d5f7b578be109b4e822aaeb921fe..b28c82a642e99186aae4ccfb42002ed989ec8c2c 100644
--- a/lib/modules/manager/sbt/extract.ts
+++ b/lib/modules/manager/sbt/extract.ts
@@ -394,6 +394,7 @@ export async function extractAllPackageFiles(
   }
   for (const pkg of packages) {
     for (const dep of pkg.deps) {
+      dep.registryUrls ??= [];
       if (proxyUrls.length > 0) {
         dep.registryUrls!.unshift(...proxyUrls);
       } else if (dep.depType === 'plugin') {