diff --git a/lib/src/kdbx_entry.dart b/lib/src/kdbx_entry.dart
index edd5628..338f3e0 100644
--- a/lib/src/kdbx_entry.dart
+++ b/lib/src/kdbx_entry.dart
@@ -77,6 +77,11 @@ extension KdbxEntryInternal on KdbxEntry {
       other._overwriteNodes,
     );
     // overwrite all strings
+    final stringsDiff = _diffMap(_strings, other._strings);
+    if (stringsDiff.isNotEmpty) {
+      overwriteContext.trackChange(this,
+          node: 'strings', debug: 'changed: ${stringsDiff.join(',')}');
+    }
     _strings.clear();
     _strings.addAll(other._strings);
     // overwrite all binaries
@@ -94,6 +99,17 @@ extension KdbxEntryInternal on KdbxEntry {
       }
     }
   }
+
+  List<String> _diffMap(Map<Object, Object> a, Map<Object, Object> b) {
+    final keys = {...a.keys, ...b.keys};
+    final ret = <String>[];
+    for (final key in keys) {
+      if (a[key] != b[key]) {
+        ret.add(key.toString());
+      }
+    }
+    return ret;
+  }
 }
 
 class KdbxEntry extends KdbxObject {
@@ -337,9 +353,11 @@ class KdbxEntry extends KdbxObject {
   void merge(MergeContext mergeContext, KdbxEntry other) {
     assertSameUuid(other, 'merge');
     if (other.wasModifiedAfter(this)) {
+      _logger.finest('$this has incoming changes.');
       // other object is newer, create new history entry and copy fields.
       modify(() => _overwriteFrom(mergeContext, other));
     } else if (wasModifiedAfter(other)) {
+      _logger.finest('$this has outgoing changes.');
       // we are newer. check if the old revision lives on in our history.
       final ourLastModificationTime = times.lastModificationTime.get();
       final historyEntry = _findHistoryEntry(history, ourLastModificationTime);
@@ -348,6 +366,8 @@ class KdbxEntry extends KdbxObject {
         // it to history.
         history.add(other.cloneInto(parent, toHistoryEntry: true));
       }
+    } else {
+      _logger.finest('$this has no changes.');
     }
     // copy missing history entries.
     for (final otherHistoryEntry in other.history) {
@@ -367,6 +387,6 @@ class KdbxEntry extends KdbxObject {
 
   @override
   String toString() {
-    return 'KdbxGroup{uuid=$uuid,name=$label}';
+    return 'KdbxEntry{uuid=$uuid,name=$label}';
   }
 }
diff --git a/lib/src/kdbx_file.dart b/lib/src/kdbx_file.dart
index 3477872..888e422 100644
--- a/lib/src/kdbx_file.dart
+++ b/lib/src/kdbx_file.dart
@@ -123,12 +123,12 @@ class KdbxFile {
   /// Merges the given file into this file.
   /// Both files must have the same origin (ie. same root group UUID).
   /// FIXME: THiS iS NOT YET FINISHED, DO NOT USE.
-  void merge(KdbxFile other) {
+  MergeContext merge(KdbxFile other) {
     if (other.body.rootGroup.uuid != body.rootGroup.uuid) {
       throw KdbxUnsupportedException(
           'Root groups of source and dest file do not match.');
     }
-    body.merge(other.body);
+    return body.merge(other.body);
   }
 }
 
diff --git a/lib/src/kdbx_format.dart b/lib/src/kdbx_format.dart
index 96bff0b..46a55c9 100644
--- a/lib/src/kdbx_format.dart
+++ b/lib/src/kdbx_format.dart
@@ -302,7 +302,7 @@ class KdbxBody extends KdbxNode {
       concat([rootGroup.getAllGroups(), rootGroup.getAllEntries()])
           .map((e) => MapEntry(e.uuid, e)));
 
-  void merge(KdbxBody other) {
+  MergeContext merge(KdbxBody other) {
     // sync deleted objects.
     final deleted =
         Map.fromEntries(ctx._deletedObjects.map((e) => MapEntry(e.uuid, e)));
@@ -341,7 +341,7 @@ class KdbxBody extends KdbxNode {
 
     // FIXME do some cleanup.
 
-    _logger.info('Finished merging. ${mergeContext.debugChanges()}');
+    _logger.info('Finished merging:\n${mergeContext.debugChanges()}');
     final incomingObjects = other._createObjectIndex();
     _logger.info('Merged: ${mergeContext.merged} vs. '
         '(local objects: ${mergeContext.objectIndex.length}, '
@@ -351,6 +351,7 @@ class KdbxBody extends KdbxNode {
     if (mergeContext.merged.keys.length != mergeContext.objectIndex.length) {
       // TODO figure out what went wrong.
     }
+    return mergeContext;
   }
 
   xml.XmlDocument generateXml(ProtectedSaltGenerator saltGenerator) {
@@ -419,6 +420,10 @@ class MergeChange {
   /// the name of the subnode of [object].
   final String node;
   final String debug;
+
+  String debugString() {
+    return [node, debug].where((e) => e != null).join(' ');
+  }
 }
 
 class MergeContext implements OverwriteContext {
@@ -451,8 +456,7 @@ class MergeContext implements OverwriteContext {
     return group.entries
         .map((e) => [
               e.key.toString(),
-              ':    ',
-              ...e.value.map((e) => e.toString()),
+              ...e.value.map((e) => e.debugString()),
             ].join('\n    '))
         .join('\n');
   }
diff --git a/lib/src/kdbx_group.dart b/lib/src/kdbx_group.dart
index 2af4ea6..4c1d8a7 100644
--- a/lib/src/kdbx_group.dart
+++ b/lib/src/kdbx_group.dart
@@ -124,6 +124,7 @@ class KdbxGroup extends KdbxObject {
       other._entries,
       importToHere: (other) => other.cloneInto(this),
     );
+    mergeContext.markAsMerged(this);
   }
 
   void _mergeSubObjects<T extends KdbxObject>(
@@ -161,7 +162,6 @@ class KdbxGroup extends KdbxObject {
         meObj.merge(mergeContext, otherObj);
       }
     }
-    mergeContext.markAsMerged(this);
   }
 
   List<KdbxSubNode> get _overwriteNodes => [
diff --git a/test/merge/kdbx_merge_test.dart b/test/merge/kdbx_merge_test.dart
new file mode 100644
index 0000000..a758fd8
--- /dev/null
+++ b/test/merge/kdbx_merge_test.dart
@@ -0,0 +1,70 @@
+import 'package:clock/clock.dart';
+import 'package:kdbx/kdbx.dart';
+import 'package:test/test.dart';
+
+import '../internal/test_utils.dart';
+import 'package:logging/logging.dart';
+
+final _logger = Logger('kdbx_merge_test');
+
+void main() {
+  TestUtil.setupLogging();
+  DateTime now = DateTime.fromMillisecondsSinceEpoch(0);
+
+  final fakeClock = Clock(() => now);
+  final kdbxFormat = TestUtil.kdbxFormat();
+  void proceedSeconds(int seconds) {
+    now = now.add(Duration(seconds: seconds));
+  }
+
+  setUp(() {
+    DateTime.fromMillisecondsSinceEpoch(0);
+  });
+  group('Simple merges', () {
+    test('Noop merge', () async {
+      final file = kdbxFormat.create(
+          Credentials.composite(ProtectedValue.fromString('asdf'), null),
+          'example');
+      _createEntry(file, file.body.rootGroup, 'test1', 'test1');
+      final file2 = await TestUtil.saveAndRead(file);
+      final merge = file.merge(file2);
+      final set = Set<KdbxUuid>.from(merge.merged.keys);
+      expect(set, hasLength(2));
+      expect(merge.changes, isEmpty);
+    });
+    test('Username change', () async {
+      await withClock(fakeClock, () async {
+        final file = kdbxFormat.create(
+            Credentials.composite(ProtectedValue.fromString('asdf'), null),
+            'example');
+        _createEntry(file, file.body.rootGroup, 'test1', 'test1');
+
+        final fileMod = await TestUtil.saveAndRead(file);
+        proceedSeconds(10);
+
+        fileMod.body.rootGroup.entries.first
+            .setString(KdbxKey('UserName'), PlainValue('changed.'));
+        _logger.info('mod date: ' +
+            fileMod.body.rootGroup.entries.first.times.lastModificationTime
+                .get()
+                .toString());
+        final file2 = await TestUtil.saveAndRead(fileMod);
+
+        _logger.info('\n\n\nstarting merge.\n');
+        final merge = file.merge(file2);
+        final set = Set<KdbxUuid>.from(merge.merged.keys);
+        expect(set, hasLength(2));
+        expect(merge.changes, hasLength(1));
+      });
+    });
+  });
+}
+
+KdbxEntry _createEntry(
+    KdbxFile file, KdbxGroup group, String username, String password) {
+  final entry = KdbxEntry.create(file, group);
+  group.addEntry(entry);
+  entry.setString(KdbxKey('UserName'), PlainValue(username));
+  entry.setString(KdbxKey('Password'), ProtectedValue.fromString(password));
+  return entry;
+}