2 files changed, 7 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 3c9510e469..c1d846f58d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -506,6 +506,10 @@ module ActiveRecord
         @connection
       end
 
+      def default_uniqueness_comparison(attribute, value) # :nodoc:
+        case_sensitive_comparison(attribute, value)
+      end
+
       def case_sensitive_comparison(attribute, value) # :nodoc:
         attribute.eq(value)
       end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index fb745af125..88ae62c681 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -12,7 +12,7 @@ module ActiveRecord
           raise ArgumentError, "#{options[:scope]} is not supported format for :scope option. " \
             "Pass a symbol or an array of symbols instead: `scope: :user_id`"
         end
-        super({ case_sensitive: true }.merge!(options))
+        super
         @klass = options[:class]
       end
 
@@ -62,6 +62,8 @@ module ActiveRecord
 
           if bind.nil?
             attr.eq(bind)
+          elsif !options.key?(:case_sensitive)
+            klass.connection.default_uniqueness_comparison(attr, bind)
           elsif options[:case_sensitive]
             klass.connection.case_sensitive_comparison(attr, bind)
           else