diff --git a/example/animal-service/Gemfile b/example/animal-service/Gemfile
index db639d15..3259665d 100644
--- a/example/animal-service/Gemfile
+++ b/example/animal-service/Gemfile
@@ -10,4 +10,4 @@ gem 'rake'
 gem 'rack', '~> 2.2', '>= 2.2.6.4'
 gem 'sqlite3'
 gem 'sequel'
-gem 'sinatra'
+gem 'sinatra', '>= 4.0.0'