diff --git a/Gemfile b/Gemfile
index 25b466eb..565aad0e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 # Specify your gem's dependencies in active_model_serializers.gemspec
 gemspec
 
-gem "minitest"
+gem "minitest", "~>5.1"
 
 version = ENV["RAILS_VERSION"] || "4.1"