diff --git a/lib/pgtk/pool.rb b/lib/pgtk/pool.rb
index c40ee28..01d309f 100644
--- a/lib/pgtk/pool.rb
+++ b/lib/pgtk/pool.rb
@@ -124,9 +124,14 @@ def transaction
     connect do |c|
       t = Txn.new(c, @log)
       t.exec('START TRANSACTION')
-      r = yield t
-      t.exec('COMMIT')
-      r
+      begin
+        r = yield t
+        t.exec('COMMIT')
+        r
+      rescue StandardError => e
+        t.exec('ROLLBACK')
+        raise e
+      end
     end
   end
 
diff --git a/test/test_pool.rb b/test/test_pool.rb
index 01f29c1..76922c0 100644
--- a/test/test_pool.rb
+++ b/test/test_pool.rb
@@ -101,6 +101,8 @@ def test_transaction_with_error
         end
       end
       assert(pool.exec('SELECT * FROM book').empty?)
+      pool.exec('INSERT INTO book (title) VALUES ($1)', ['another'])
+      assert(!pool.exec('SELECT * FROM book').empty?)
     end
   end