diff --git a/src/Database.cpp b/src/Database.cpp
index 640a127b..e6245149 100644
--- a/src/Database.cpp
+++ b/src/Database.cpp
@@ -176,7 +176,9 @@ void Database::modifyInterval (const Interval& from, const Interval& to)
 void Database::undoTxnStart ()
 {
   if (_txn == 0)
-    _undo.push_back ("txn:");
+  {
+    _currentTransaction = std::make_shared <Transaction> ();
+  }
 
   ++_txn;
 }
@@ -191,16 +193,18 @@ void Database::undoTxnEnd ()
   if (_txn == 0)
   {
     File undo (_location + "/undo.data");
+
     if (undo.open ())
     {
-      for (auto& line : _undo)
-        undo.append (line + "\n");
+      undo.append (_currentTransaction->toString());
 
       undo.close ();
-      _undo.clear ();
+      _currentTransaction.reset ();
     }
     else
+    {
       throw format ("Unable to write the undo transaction to {1}", undo._data);
+    }
   }
 }
 
@@ -213,9 +217,7 @@ void Database::undoTxn (
   const std::string& before,
   const std::string& after)
 {
-  _undo.push_back ("  type: " + type);
-  _undo.push_back ("  before: " + before);
-  _undo.push_back ("  after: " + after);
+  _currentTransaction->addUndoAction (type, before, after);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/Database.h b/src/Database.h
index 26e0e80c..01e0779e 100644
--- a/src/Database.h
+++ b/src/Database.h
@@ -30,6 +30,7 @@
 #include <Datafile.h>
 #include <Interval.h>
 #include <Range.h>
+#include <Transaction.h>
 #include <vector>
 #include <string>
 
@@ -62,8 +63,9 @@ private:
 private:
   std::string               _location {"~/.timewarrior/data"};
   std::vector <Datafile>    _files    {};
-  std::vector <std::string> _undo     {};
   int                       _txn      {0};
+
+  std::shared_ptr <Transaction> _currentTransaction = nullptr;
 };
 
 #endif
diff --git a/src/Transaction.cpp b/src/Transaction.cpp
index 93fc1635..194d8416 100644
--- a/src/Transaction.cpp
+++ b/src/Transaction.cpp
@@ -34,3 +34,15 @@ void Transaction::addUndoAction (
 {
    _actions.emplace_back (type, before, after);
 }
+
+std::string Transaction::toString ()
+{
+  std::string output = "txn:\n";
+
+  for (auto& action : _actions)
+  {
+    output += action.toString ();
+  }
+
+  return output;
+}
diff --git a/src/Transaction.h b/src/Transaction.h
index e58c851d..4a1dce86 100644
--- a/src/Transaction.h
+++ b/src/Transaction.h
@@ -35,6 +35,8 @@ class Transaction
 public:
   void addUndoAction(const std::string&, const std::string&, const std::string&);
 
+  std::string toString();
+
 private:
   std::vector<UndoAction> _actions {};
 };
diff --git a/src/UndoAction.cpp b/src/UndoAction.cpp
index 4b989f06..5b6d9d02 100644
--- a/src/UndoAction.cpp
+++ b/src/UndoAction.cpp
@@ -35,3 +35,10 @@ UndoAction::UndoAction (
   _before = before;
   _after = after;
 }
+
+std::string UndoAction::toString ()
+{
+  return "  type: " + _type + "\n" +
+         "  before: " + _before + "\n" +
+         "  after: " + _after + "\n";
+}
diff --git a/src/UndoAction.h b/src/UndoAction.h
index 3236505f..97ebd27a 100644
--- a/src/UndoAction.h
+++ b/src/UndoAction.h
@@ -34,6 +34,8 @@ class UndoAction
 public:
   UndoAction(const std::string&, const std::string&, const std::string&);
 
+  std::string toString ();
+
 private:
   std::string _type;
   std::string _before;