diff --git a/active_model_serializers.gemspec b/active_model_serializers.gemspec
index 0009a94ee..cc57936ab 100644
--- a/active_model_serializers.gemspec
+++ b/active_model_serializers.gemspec
@@ -55,7 +55,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'kaminari', ' ~> 0.16.3'
   spec.add_development_dependency 'will_paginate', '~> 3.0', '>= 3.0.7'
 
-  spec.add_development_dependency 'bundler', '~> 1.6'
+  spec.add_development_dependency 'bundler', '> 1.6'
   spec.add_development_dependency 'simplecov', '~> 0.11'
   spec.add_development_dependency 'timecop', '~> 0.7'
   spec.add_development_dependency 'grape', ['>= 0.13', '< 0.19.1']
diff --git a/appveyor.yml b/appveyor.yml
index 1fc009903..0bfd865a9 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -4,9 +4,10 @@ skip_tags: true
 
 environment:
   JRUBY_OPTS: "--dev -J-Xmx1024M --debug"
+  RAILS_VERSION: 5.2
   matrix:
-    - ruby_version: "Ruby23"
-    - ruby_version: "Ruby23-x64"
+    - ruby_version: "Ruby25"
+    - ruby_version: "Ruby25-x64"
 
 cache:
   - vendor/bundle