IrreversibleMigration is raised if we cannot invert the command

activerecord/lib/active_record/migration/command_recorder.rb

@@ -20,7 +20,11 @@ module ActiveRecord
       # Returns a list that represents commands that are the inverse of the
       # commands stored in +commands+.
       def inverse
-        @commands.reverse.map { |name, args| send(:"invert_#{name}", args) }
+        @commands.reverse.map { |name, args|
+          method = :"invert_#{name}"
+          raise IrreversibleMigration unless respond_to?(method, true)
+          send(method, args)
+        }
       end
 
       private

activerecord/test/cases/migration/command_recorder_test.rb

@@ -7,6 +7,13 @@ module ActiveRecord
         @recorder = CommandRecorder.new
       end
 
+      def test_unknown_commands_raise_exception
+        @recorder.record :execute, ['some sql']
+        assert_raises(ActiveRecord::IrreversibleMigration) do
+          @recorder.inverse
+        end
+      end
+
       def test_record
         @recorder.record :create_table, [:system_settings]
         assert_equal 1, @recorder.commands.length