diff --git a/lib/platform/gitlab/index.ts b/lib/platform/gitlab/index.ts
index 17e8a527fcb95d0b3da8f5d4bd3df308e5ce11cc..e86f7cb09272855800f4116a8f1833a47f2e2441 100644
--- a/lib/platform/gitlab/index.ts
+++ b/lib/platform/gitlab/index.ts
@@ -202,7 +202,7 @@ export async function initRepo({
     }
     config.defaultBranch = res.body.default_branch;
     config.baseBranch = config.defaultBranch;
-    config.mergeMethod = res.body.merge_method;
+    config.mergeMethod = res.body.merge_method || 'merge';
     logger.debug(`${repository} default branch = ${config.baseBranch}`);
     // Discover our user email
     config.email = (await api.get(`user`)).body.email;