diff --git a/lib/ruby_http_client.rb b/lib/ruby_http_client.rb
index 495f498..4b5517c 100644
--- a/lib/ruby_http_client.rb
+++ b/lib/ruby_http_client.rb
@@ -184,7 +184,7 @@ def build_args(args)
     #   - The final url string
     #
     def build_url(query_params: nil)
-      url = [add_version(''), *@url_path].join('/')
+      url = [add_version(+''), *@url_path].join('/')
       url = build_query_params(url, query_params) if query_params
       URI.parse("#{@host}#{url}")
     end