diff --git a/lib/workers/repository/index.js b/lib/workers/repository/index.js
index fa068fe5b61eab3f9d40a5d78716e66a827a0ae7..a590265bb1fe04ab09b59084768582d20e7208c0 100644
--- a/lib/workers/repository/index.js
+++ b/lib/workers/repository/index.js
@@ -49,6 +49,7 @@ async function renovateRepository(repoConfig, token) {
     }
     if (config.isFork && !config.renovateJsonPresent) {
       logger.debug('repository is a fork and not manually configured');
+      await cleanup.pruneStaleBranches(config, []);
       return null;
     }
     if (config.baseBranch) {