diff --git a/app/models/site/repository.rb b/app/models/site/repository.rb
index 43dae27..74db254 100644
--- a/app/models/site/repository.rb
+++ b/app/models/site/repository.rb
@@ -161,12 +161,12 @@ class Site
 
     # @return [String]
     def public_key
-      @public_key ||= Rails.root.join('.ssh', 'id_ed25519.pub')
+      @public_key ||= Rails.root.join('.ssh', 'id_ed25519.pub').to_s
     end
 
     # @return [String]
     def private_key
-      @private_key ||= Rails.root.join('.ssh', 'id_ed25519')
+      @private_key ||= Rails.root.join('.ssh', 'id_ed25519').to_s
     end
 
     def relativize(file)