diff --git a/README.md b/README.md
index 0f193e8c..f18f9f30 100644
--- a/README.md
+++ b/README.md
@@ -71,7 +71,7 @@ Or install it yourself as:
 
 Then tell your ruby web application to use rack-attack as a middleware.
 
-a) For __rails__ applications with versions >= 5 it is used by default. For older rails versions you should enable it explicitly:
+a) For __rails__ applications with versions >= 5.1 it is used by default. For older rails versions you should enable it explicitly:
 ```ruby
 # In config/application.rb
 
diff --git a/lib/rack/attack/railtie.rb b/lib/rack/attack/railtie.rb
index 59994f1c..ceed9f7d 100644
--- a/lib/rack/attack/railtie.rb
+++ b/lib/rack/attack/railtie.rb
@@ -4,7 +4,7 @@ module Rack
   class Attack
     class Railtie < ::Rails::Railtie
       initializer 'rack.attack.middleware', after: :load_config_initializers, before: :build_middleware_stack do |app|
-        if Gem::Version.new(::Rails::VERSION::STRING) >= Gem::Version.new("5")
+        if Gem::Version.new(::Rails::VERSION::STRING) >= Gem::Version.new("5.1")
           middlewares = app.config.middleware
           operations = middlewares.send(:operations) + middlewares.send(:delete_operations)
 
diff --git a/spec/acceptance/rails_middleware_spec.rb b/spec/acceptance/rails_middleware_spec.rb
index 4d27c702..2c69b7e1 100644
--- a/spec/acceptance/rails_middleware_spec.rb
+++ b/spec/acceptance/rails_middleware_spec.rb
@@ -12,7 +12,7 @@
       end
     end
 
-    if Gem::Version.new(Rails::VERSION::STRING) >= Gem::Version.new("5")
+    if Gem::Version.new(Rails::VERSION::STRING) >= Gem::Version.new("5.1")
       it "is used by default" do
         @app.initialize!
         assert_equal 1, @app.middleware.count(Rack::Attack)
@@ -31,7 +31,7 @@
       end
     end
 
-    if Gem::Version.new(Rails::VERSION::STRING) < Gem::Version.new("5")
+    if Gem::Version.new(Rails::VERSION::STRING) < Gem::Version.new("5.1")
       it "is not used by default" do
         @app.initialize!
         assert_equal 0, @app.middleware.count(Rack::Attack)