diff --git a/lib/modulesync/repository.rb b/lib/modulesync/repository.rb
index 1e50848..ed6d57c 100644
--- a/lib/modulesync/repository.rb
+++ b/lib/modulesync/repository.rb
@@ -40,6 +40,9 @@ def default_branch
     def switch(branch:)
       unless branch
         branch = default_branch
+        unless branch
+          raise "Unable to detect default branch"
+        end
         puts "Using repository's default branch: #{branch}"
       end
       return if repo.current_branch == branch