diff --git a/README.md b/README.md
index 38631fd..3321c9c 100644
--- a/README.md
+++ b/README.md
@@ -28,22 +28,25 @@ Include `omemo_dart` in your `pubspec.yaml` like this:
 dependencies:
   omemo_dart:
     hosted: https://git.polynom.me/api/packages/PapaTutuWawa/pub
-    version: ^0.4.3
+    version: ^0.5.0
   # [...]
 
 # [...]
 ```
 
-## Contributing
+### Persistence
 
-Due to issues with `protobuf`, `omemo_dart` reimplements the Protobuf encoding for the required
-OMEMO messages. As such, `protobuf` is only a dependency for testing that the serialisation and
-deserialisation of the custom implementation. In order to run tests, you need the Protbuf
-compiler. After that, making sure that
-the [Dart Protobuf compiler addon](https://pub.dev/packages/protoc_plugin) and the
-Protobuf compiler itself is in your PATH,
-run `protoc -I=./protobuf/ --dart_out=lib/protobuf/ ./protobuf/schema.proto` in the
-repository's root to generate the real Protobuf bindings.
+By default, `omemo_dart` uses in-memory implementations for everything. For a real-world application, this is unsuitable as OMEMO devices would be constantly added.
+In order to allow persistence, your application needs to keep track of the following mappings:
+
+- `JID -> [int]`: The device list for each JID
+- `(JID, device) -> Ratchet`: The actual ratchet
+
+If you also use the `BlindTrustBeforeVerificationTrustManager`, you additionally need to keep track of:
+
+- `(JID, device) -> (int, bool)`: The trust level and the enablement state
+
+## Contributing
 
 When submitting a PR, please run the linter using `dart analyze` and make sure that all
 tests still pass using `dart test`.
diff --git a/lib/src/helpers.dart b/lib/src/helpers.dart
index 287010f..bbf2cbd 100644
--- a/lib/src/helpers.dart
+++ b/lib/src/helpers.dart
@@ -86,9 +86,13 @@ extension BeforeAfterListDiff<T> on List<T> {
 
 extension AppendToListOrCreateExtension<K, V> on Map<K, List<V>> {
   /// Create or append [value] to the list identified with key [key].
-  void appendOrCreate(K key, V value) {
+  void appendOrCreate(K key, V value, {bool checkExistence = false}) {
     if (containsKey(key)) {
-      this[key]!.add(value);
+      if (!checkExistence) {
+        this[key]!.add(value);
+      } if (!this[key]!.contains(value)) {
+        this[key]!.add(value);
+      }
     } else {
       this[key] = [value];
     }
diff --git a/lib/src/trust/btbv.dart b/lib/src/trust/btbv.dart
index 4eb1365..5a04ab8 100644
--- a/lib/src/trust/btbv.dart
+++ b/lib/src/trust/btbv.dart
@@ -132,11 +132,8 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
       enablementCache[key] = true;
     }
 
-    if (devices.containsKey(jid)) {
-      devices[jid]!.add(deviceId);
-    } else {
-      devices[jid] = List<int>.from([deviceId]);
-    }
+    // Append to the device list
+    devices.appendOrCreate(jid, deviceId, checkExistence: true);
 
     // Commit the state
     await commit(
@@ -227,7 +224,7 @@ class BlindTrustBeforeVerificationTrustManager extends TrustManager {
       final key = RatchetMapKey(jid, result.device);
       trustCache[key] = result.state;
       enablementCache[key] = result.enabled;
-      devices.appendOrCreate(jid, result.device);
+      devices.appendOrCreate(jid, result.device, checkExistence: true);
     }
   }