diff --git a/.travis.yml b/.travis.yml
index c98d274..d696151 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,7 @@
 language: ruby
 rvm:
+  - 2.4.0
+  - 2.3.3
   - 2.2.0
   - 2.1.5
   - 2.1.4
@@ -14,6 +16,12 @@ jdk: # for JRuby only
   - oraclejdk8
 matrix:
   exclude:
+    - rvm: 2.4.0
+      jdk: openjdk7
+      jdk: oraclejdk8
+    - rvm: 2.3.3
+      jdk: openjdk7
+      jdk: oraclejdk8
     - rvm: 2.2.0
       jdk: openjdk7
       jdk: oraclejdk8
@@ -40,4 +48,4 @@ matrix:
     - rvm: jruby-head
     - rvm: 1.9.3
 
-script: "rake test"
+script: "bundle exec rake test"
diff --git a/Gemfile b/Gemfile
index 2ad2b76..e5cb94c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,6 +5,7 @@ gemspec
 group :development, :test do
   gem 'rspec', '~> 3.2.0'
   gem 'simplecov', '~> 0.9.2', :require => false
+  gem 'tins', '~> 1.10.2', :require => false
   gem 'coveralls', '~> 0.7.11', :require => false
 end
 
diff --git a/lib/thread_safe/cache.rb b/lib/thread_safe/cache.rb
index 109cb98..265c0e5 100644
--- a/lib/thread_safe/cache.rb
+++ b/lib/thread_safe/cache.rb
@@ -150,8 +150,8 @@ def populate_from(hash)
     end
 
     def validate_options_hash!(options)
-      if (initial_capacity = options[:initial_capacity]) && (!initial_capacity.kind_of?(Fixnum) || initial_capacity < 0)
-        raise ArgumentError, ":initial_capacity must be a positive Fixnum"
+      if (initial_capacity = options[:initial_capacity]) && (!initial_capacity.kind_of?(0.class) || initial_capacity < 0)
+        raise ArgumentError, ":initial_capacity must be a positive #{0.class}"
       end
       if (load_factor = options[:load_factor]) && (!load_factor.kind_of?(Numeric) || load_factor <= 0 || load_factor > 1)
         raise ArgumentError, ":load_factor must be a number between 0 and 1"
diff --git a/thread_safe.gemspec b/thread_safe.gemspec
index 5e6aba1..cf3faeb 100644
--- a/thread_safe.gemspec
+++ b/thread_safe.gemspec
@@ -21,6 +21,6 @@ Gem::Specification.new do |gem|
   gem.license       = "Apache-2.0"
 
   gem.add_development_dependency 'atomic', '= 1.1.16'
-  gem.add_development_dependency 'rake'
+  gem.add_development_dependency 'rake', '< 12.0'
   gem.add_development_dependency 'rspec', '~> 3.2'
 end