diff --git a/.travis.yml b/.travis.yml
index 4b4449b395..ca4e706125 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,11 +3,15 @@ language: ruby
 sudo: false
 cache: bundler
 env: CODECLIMATE_REPO_TOKEN=f5b27b2e25d3f4e199bb2566fb4fd4507144a004c71d4aa33a32c2df5f940333
+before_install:
+  - gem update --system --no-doc
+  - gem install bundler
 
 rvm:
 - 2.1.0 # Lowest version officially supported by that gem
 - 2.2.5
-- 2.3.1
+- 2.3.3
+- 2.4.0
 
 gemfile:
 - gemfiles/rails_3.2.gemfile
@@ -17,5 +21,11 @@ gemfile:
 
 matrix:
   exclude:
+  - rvm: 2.4.0
+    gemfile: gemfiles/rails_3.2.gemfile
+  - rvm: 2.4.0
+    gemfile: gemfiles/rails_4.1.gemfile
+  - rvm: 2.4.0
+    gemfile: gemfiles/rails_4.2.gemfile
   - rvm: 2.1.0
     gemfile: gemfiles/rails_5.0.gemfile # Rails 5 requires Ruby 2.2.2+
diff --git a/lib/graphql/id_type.rb b/lib/graphql/id_type.rb
index 96ab15aaee..b4fa599688 100644
--- a/lib/graphql/id_type.rb
+++ b/lib/graphql/id_type.rb
@@ -6,7 +6,7 @@
   coerce_result ->(value) { value.to_s }
   coerce_input ->(value) {
     case value
-    when String, Fixnum, Bignum
+    when String, Integer
       value.to_s
     else
       nil
diff --git a/spec/graphql/schema/validation_spec.rb b/spec/graphql/schema/validation_spec.rb
index 40c484fb3e..43f9b8c242 100644
--- a/spec/graphql/schema/validation_spec.rb
+++ b/spec/graphql/schema/validation_spec.rb
@@ -2,6 +2,10 @@
 require "spec_helper"
 
 describe GraphQL::Schema::Validation do
+  def integer_class_name
+    RUBY_VERSION >= "2.4.0" ? "Integer" : "Fixnum"
+  end
+
   def assert_error_includes(object, error_substring)
     validation_error = GraphQL::Schema::Validation.validate(object)
     assert_includes validation_error, error_substring
@@ -102,7 +106,7 @@ def assert_validation_warns(object, warning)
     end
 
     it "requires String-or-nil description" do
-      assert_error_includes wrongly_described_type, "must return String or NilClass, not Fixnum"
+      assert_error_includes wrongly_described_type, "must return String or NilClass, not #{integer_class_name}"
     end
   end
 
@@ -129,7 +133,7 @@ def assert_validation_warns(object, warning)
     }
 
     it "requires an Array for interfaces" do
-      assert_error_includes invalid_interfaces_object, "must be an Array of GraphQL::InterfaceType, not a Fixnum"
+      assert_error_includes invalid_interfaces_object, "must be an Array of GraphQL::InterfaceType, not a #{integer_class_name}"
       assert_error_includes invalid_interface_member_object, "must contain GraphQL::InterfaceType, not Symbol"
     end
 
@@ -163,7 +167,7 @@ def assert_validation_warns(object, warning)
     }
 
     it "requires an array of ObjectTypes for possible_types" do
-      assert_error_includes non_array_union, "must be an Array of GraphQL::ObjectType, not a Fixnum"
+      assert_error_includes non_array_union, "must be an Array of GraphQL::ObjectType, not a #{integer_class_name}"
 
       assert_error_includes non_object_type_union, "must contain GraphQL::ObjectType, not GraphQL::InterfaceType"
     end
@@ -193,7 +197,7 @@ def assert_validation_warns(object, warning)
     }
 
     it "requires {String => Argument} arguments" do
-      assert_error_includes invalid_arguments_input, "map String => GraphQL::Argument, not Fixnum => Symbol"
+      assert_error_includes invalid_arguments_input, "map String => GraphQL::Argument, not #{integer_class_name} => Symbol"
     end
 
     it "applies validation to its member Arguments" do