diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index c675b64a269a8..d2126a3e198cc 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -1189,7 +1189,7 @@ def distinct(columns, orders) #:nodoc:
 
         # 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*/i, '') }
+        order_columns = orders.collect { |s| s.gsub(/\s+(ASC|DESC)\s*(NULLS\s+(FIRST|LAST)\s*)?/i, '') }
         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/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index 898d28456b6e5..a71d0bb848eca 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -185,6 +185,11 @@ def test_partial_index
         assert_equal "(number > 100)", index.where
       end
 
+      def test_distinct_with_nulls
+        assert_equal "DISTINCT posts.title, posts.updater_id AS alias_0", @connection.distinct("posts.title", ["posts.updater_id desc nulls first"])
+        assert_equal "DISTINCT posts.title, posts.updater_id AS alias_0", @connection.distinct("posts.title", ["posts.updater_id desc nulls last"])
+      end
+
       private
       def insert(ctx, data)
         binds   = data.map { |name, value|