diff --git a/lib/src/cross_signing.dart b/lib/src/cross_signing.dart
index cb247cf..ab9f018 100644
--- a/lib/src/cross_signing.dart
+++ b/lib/src/cross_signing.dart
@@ -55,7 +55,9 @@ class CrossSigning {
         signatures[key.userId] = <String, dynamic>{};
       }
       if (!signatures[key.userId].containsKey(key.identifier)) {
-        signatures[key.userId][key.identifier] = key.toJson();
+        signatures[key.userId][key.identifier] =
+            Map<String, dynamic>.from(key.toJson());
+        signatures[key.userId][key.identifier].remove('signatures');
       }
       if (!signatures[key.userId][key.identifier].containsKey('signatures')) {
         signatures[key.userId][key.identifier]
@@ -79,18 +81,19 @@ class CrossSigning {
             final signature = client.signString(key.signingContent);
             addSignature(
                 key,
-                client.userDeviceKeys[client.userID].deviceKeys[client.deviceID],
+                client
+                    .userDeviceKeys[client.userID].deviceKeys[client.deviceID],
                 signature);
           }
           // we don't care about signing other cross-signing keys
         } else if (key.identifier != client.deviceID) {
           // okay, we'll sign a device key with our self signing key
-          selfSigningKey ??=
-              base64.decode(await client.ssss.getCached(SELF_SIGNING_KEY) ?? '');
+          selfSigningKey ??= base64
+              .decode(await client.ssss.getCached(SELF_SIGNING_KEY) ?? '');
           if (selfSigningKey != null) {
             final signature = _sign(key.signingContent, selfSigningKey);
-            addSignature(key, client.userDeviceKeys[client.userID].selfSigningKey,
-                signature);
+            addSignature(key,
+                client.userDeviceKeys[client.userID].selfSigningKey, signature);
           }
         }
       } else if (key is CrossSigningKey && key.usage.contains('master')) {
@@ -99,8 +102,8 @@ class CrossSigning {
             base64.decode(await client.ssss.getCached(USER_SIGNING_KEY) ?? '');
         if (userSigningKey != null) {
           final signature = _sign(key.signingContent, userSigningKey);
-          addSignature(
-              key, client.userDeviceKeys[client.userID].userSigningKey, signature);
+          addSignature(key, client.userDeviceKeys[client.userID].userSigningKey,
+              signature);
         }
       }
     }
diff --git a/lib/src/utils/key_verification.dart b/lib/src/utils/key_verification.dart
index d0d9d6c..de501b4 100644
--- a/lib/src/utils/key_verification.dart
+++ b/lib/src/utils/key_verification.dart
@@ -362,8 +362,8 @@ class KeyVerification {
     if (verifiedMasterKey && userId == client.userID) {
       // it was our own master key, let's request the cross signing keys
       // we do it in the background, thus no await needed here
-      unawaited(client.ssss.maybeRequestAll(
-          _verifiedDevices.whereType<DeviceKeys>().toList()));
+      unawaited(client.ssss
+          .maybeRequestAll(_verifiedDevices.whereType<DeviceKeys>().toList()));
     }
     await send('m.key.verification.done', {});
 
@@ -727,6 +727,17 @@ class _KeyVerificationMethodSas extends _KeyVerificationMethod {
         _calculateMac(client.fingerprintKey, baseInfo + deviceKeyId);
     keyList.add(deviceKeyId);
 
+    final masterKey = client.userDeviceKeys.containsKey(client.userID)
+        ? client.userDeviceKeys[client.userID].masterKey
+        : null;
+    if (masterKey != null && masterKey.verified) {
+      // we have our own master key verified, let's send it!
+      final masterKeyId = 'ed25519:${masterKey.publicKey}';
+      mac[masterKeyId] =
+          _calculateMac(masterKey.publicKey, baseInfo + masterKeyId);
+      keyList.add(masterKeyId);
+    }
+
     keyList.sort();
     final keys = _calculateMac(keyList.join(','), baseInfo + 'KEY_IDS');
     await request.send('m.key.verification.mac', {