diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 88b09e7999..2d0eef6c84 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -359,8 +359,12 @@ class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, options = {})
-          return super unless type == :uuid
-          options[:default] = options.fetch(:default, 'uuid_generate_v4()')
+          return super unless type = :primary_key
+
+          if type == :uuid
+            options[:default] = options.fetch(:default, 'uuid_generate_v4()')
+          end
+
           options[:primary_key] = true
           column name, type, options
         end
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 8e5379cb1f..a1149e410b 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -216,3 +216,32 @@ def test_primaery_key_method_with_ansi_quotes
   end
 end
 
+if current_adapter?(:PostgreSQLAdapter)
+  class PrimaryKeyBigSerialTest < ActiveRecord::TestCase
+    self.use_transactional_fixtures = false
+
+    class Widget < ActiveRecord::Base
+    end
+
+    def setup
+      @con = ActiveRecord::Base.connection
+
+      ActiveRecord::Schema.define do
+        create_table :widgets, id: :bigserial do |t|
+        end
+      end
+    end
+
+    def teardown
+      ActiveRecord::Schema.define do
+        drop_table :widgets
+      end
+    end
+
+    def test_bigserial_primary_key
+      widget = Widget.create!
+
+      assert_not_nil widget.id
+    end
+  end
+end