diff --git a/Gemfile b/Gemfile
index d7c921c74..e2eff4df8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,5 +7,5 @@ group :local_development do
   gem 'guard-rspec'
   gem 'appraisal'
   gem 'rake'
-  gem 'byebug' , platforms: [:mri_21, :mri_22, :mri_23]
+  gem 'byebug', platforms: [:mri]
 end
diff --git a/acts-as-taggable-on.gemspec b/acts-as-taggable-on.gemspec
index 534ab499c..8258c30f1 100644
--- a/acts-as-taggable-on.gemspec
+++ b/acts-as-taggable-on.gemspec
@@ -24,10 +24,6 @@ Gem::Specification.new do |gem|
 
   gem.add_runtime_dependency 'activerecord', ['~> 5.0']
 
-  gem.add_development_dependency 'sqlite3'
-  gem.add_development_dependency 'mysql2', '~> 0.3'
-  gem.add_development_dependency 'pg'
-
   gem.add_development_dependency 'rspec-rails'
   gem.add_development_dependency 'rspec-its'
   gem.add_development_dependency 'rspec'
diff --git a/gemfiles/activerecord_5.0.gemfile b/gemfiles/activerecord_5.0.gemfile
index ee23028fd..e48906999 100644
--- a/gemfiles/activerecord_5.0.gemfile
+++ b/gemfiles/activerecord_5.0.gemfile
@@ -3,6 +3,14 @@
 source "https://rubygems.org"
 
 gem "activerecord", "~> 5.0.3"
+case ENV["DB"]
+when "postgresql"
+  gem 'pg'
+when "mysql"
+  gem 'mysql2', '~> 0.3'
+else
+  gem 'sqlite3'
+end
 
 group :local_development do
   gem "guard"
diff --git a/gemfiles/activerecord_5.1.gemfile b/gemfiles/activerecord_5.1.gemfile
index ea71e58bc..ca8c1920c 100644
--- a/gemfiles/activerecord_5.1.gemfile
+++ b/gemfiles/activerecord_5.1.gemfile
@@ -3,6 +3,14 @@
 source "https://rubygems.org"
 
 gem "activerecord", "~> 5.1.1"
+case ENV["DB"]
+when "postgresql"
+  gem 'pg'
+when "mysql"
+  gem 'mysql2', '~> 0.3'
+else
+  gem 'sqlite3'
+end
 
 group :local_development do
   gem "guard"
diff --git a/gemfiles/activerecord_5.2.gemfile b/gemfiles/activerecord_5.2.gemfile
index 6b566da46..fe6525fdd 100644
--- a/gemfiles/activerecord_5.2.gemfile
+++ b/gemfiles/activerecord_5.2.gemfile
@@ -3,6 +3,14 @@
 source "https://rubygems.org"
 
 gem "activerecord", "~> 5.2.0"
+case ENV["DB"]
+when "postgresql"
+  gem 'pg'
+when "mysql"
+  gem 'mysql2', '~> 0.3'
+else
+  gem 'sqlite3'
+end
 
 group :local_development do
   gem "guard"
diff --git a/lib/acts_as_taggable_on/taggable/related.rb b/lib/acts_as_taggable_on/taggable/related.rb
index 8fb02d35a..7a9755108 100644
--- a/lib/acts_as_taggable_on/taggable/related.rb
+++ b/lib/acts_as_taggable_on/taggable/related.rb
@@ -49,7 +49,7 @@ def related_tags_for(context, klass, options = {})
     private
 
     def exclude_self(klass, id)
-      "#{klass.table_name}.#{klass.primary_key} != #{id} AND" if [self.class.base_class, self.class].include? klass
+      "#{klass.arel_table[klass.primary_key].not_eq(id).to_sql} AND" if [self.class.base_class, self.class].include? klass
     end
 
     def group_columns(klass)
diff --git a/lib/acts_as_taggable_on/taggable/tagged_with_query/query_base.rb b/lib/acts_as_taggable_on/taggable/tagged_with_query/query_base.rb
index 56481e74e..b556d70f0 100644
--- a/lib/acts_as_taggable_on/taggable/tagged_with_query/query_base.rb
+++ b/lib/acts_as_taggable_on/taggable/tagged_with_query/query_base.rb
@@ -48,7 +48,7 @@ def tags_match_type
 
     def escaped_tag(tag)
       tag = tag.downcase unless ActsAsTaggableOn.strict_case_match
-      tag.gsub(/[!%_]/) { |x| '!' + x }
+      ActsAsTaggableOn::Utils.escape_like(tag)
     end
 
     def adjust_taggings_alias(taggings_alias)
diff --git a/lib/acts_as_taggable_on/version.rb b/lib/acts_as_taggable_on/version.rb
index e311f9c59..49f8b1466 100644
--- a/lib/acts_as_taggable_on/version.rb
+++ b/lib/acts_as_taggable_on/version.rb
@@ -1,4 +1,4 @@
 module ActsAsTaggableOn
-  VERSION = '5.0.0'
+  VERSION = '6.0.0'
 end