diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 273c165084..68cf495025 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -1233,7 +1233,10 @@ module ActiveRecord
 
         # Construct a clean list of column names from the ORDER BY clause, removing
         # any ASC/DESC modifiers
-        order_columns = orders.collect { |s| s.gsub(/\s+(ASC|DESC)\s*(NULLS\s+(FIRST|LAST)\s*)?/i, '') }
+        order_columns = orders.collect do |s|
+          s = s.to_sql unless s.is_a?(String)
+          s.gsub(/\s+(ASC|DESC)\s*(NULLS\s+(FIRST|LAST)\s*)?/i, '')
+        end
         order_columns.delete_if { |c| c.blank? }
         order_columns = order_columns.zip((0...order_columns.size).to_a).map { |s,i| "#{s} AS alias_#{i}" }
 
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index d13bed95ce..3c9c9c4e84 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -91,7 +91,7 @@ module ActiveRecord
     def first(limit = nil)
       if limit
         if order_values.empty? && primary_key
-          order("#{quoted_table_name}.#{quoted_primary_key} ASC").limit(limit).to_a
+          order(arel_table[primary_key].asc).limit(limit).to_a
         else
           limit(limit).to_a
         end
@@ -117,7 +117,7 @@ module ActiveRecord
     def last(limit = nil)
       if limit
         if order_values.empty? && primary_key
-          order("#{quoted_table_name}.#{quoted_primary_key} DESC").limit(limit).reverse
+          order(arel_table[primary_key].desc).limit(limit).reverse
         else
           to_a.last(limit)
         end
@@ -362,7 +362,7 @@ module ActiveRecord
       else
         @first ||=
           if order_values.empty? && primary_key
-            order("#{quoted_table_name}.#{quoted_primary_key} ASC").limit(1).to_a.first
+            order(arel_table[primary_key].asc).limit(1).to_a.first
           else
             limit(1).to_a.first
           end