diff --git a/src/test/java/org/qortal/test/at/AtSerializationTests.java b/src/test/java/org/qortal/test/at/AtSerializationTests.java
new file mode 100644
index 00000000..3953bcdf
--- /dev/null
+++ b/src/test/java/org/qortal/test/at/AtSerializationTests.java
@@ -0,0 +1,96 @@
+package org.qortal.test.at;
+
+import com.google.common.hash.HashCode;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.qortal.account.PrivateKeyAccount;
+import org.qortal.data.transaction.ATTransactionData;
+import org.qortal.data.transaction.TransactionData;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.test.common.Common;
+import org.qortal.test.common.transaction.AtTestTransaction;
+import org.qortal.transaction.Transaction;
+import org.qortal.transform.TransformationException;
+import org.qortal.transform.transaction.TransactionTransformer;
+import org.qortal.utils.Base58;
+
+import static org.junit.Assert.assertEquals;
+
+public class AtSerializationTests extends Common {
+
+    @Before
+    public void beforeTest() throws DataException {
+        Common.useDefaultSettings();
+    }
+
+    @After
+    public void afterTest() throws DataException {
+        Common.orphanCheck();
+    }
+
+
+    @Test
+    public void testPaymentTypeAtSerialization() throws DataException, TransformationException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Build PAYMENT-type AT transaction
+            PrivateKeyAccount signingAccount = Common.getTestAccount(repository, "alice");
+            ATTransactionData transactionData = (ATTransactionData) AtTestTransaction.paymentType(repository, signingAccount, true);
+            Transaction transaction = Transaction.fromData(repository, transactionData);
+            transaction.sign(signingAccount);
+
+            final int claimedLength = TransactionTransformer.getDataLength(transactionData);
+            byte[] serializedTransaction = TransactionTransformer.toBytes(transactionData);
+            assertEquals("Serialized PAYMENT-type AT transaction length differs from declared length", claimedLength, serializedTransaction.length);
+
+            TransactionData deserializedTransactionData = TransactionTransformer.fromBytes(serializedTransaction);
+            // Re-sign
+            Transaction deserializedTransaction = Transaction.fromData(repository, deserializedTransactionData);
+            deserializedTransaction.sign(signingAccount);
+            assertEquals("Deserialized PAYMENT-type AT transaction signature differs", Base58.encode(transactionData.getSignature()), Base58.encode(deserializedTransactionData.getSignature()));
+
+            // Re-serialize to check new length and bytes
+            final int reclaimedLength = TransactionTransformer.getDataLength(deserializedTransactionData);
+            assertEquals("Reserialized PAYMENT-type AT transaction declared length differs", claimedLength, reclaimedLength);
+
+            byte[] reserializedTransaction = TransactionTransformer.toBytes(deserializedTransactionData);
+            assertEquals("Reserialized PAYMENT-type AT transaction bytes differ", HashCode.fromBytes(serializedTransaction).toString(), HashCode.fromBytes(reserializedTransaction).toString());
+        }
+    }
+
+    @Test
+    public void testMessageTypeAtSerialization() throws DataException, TransformationException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Build MESSAGE-type AT transaction
+            PrivateKeyAccount signingAccount = Common.getTestAccount(repository, "alice");
+            ATTransactionData transactionData = (ATTransactionData) AtTestTransaction.messageType(repository, signingAccount, true);
+            Transaction transaction = Transaction.fromData(repository, transactionData);
+            transaction.sign(signingAccount);
+
+            // MESSAGE-type AT transactions are only fully supported since transaction V6
+            assertEquals(6, Transaction.getVersionByTimestamp(transactionData.getTimestamp()));
+
+            final int claimedLength = TransactionTransformer.getDataLength(transactionData);
+            byte[] serializedTransaction = TransactionTransformer.toBytes(transactionData);
+            assertEquals("Serialized MESSAGE-type AT transaction length differs from declared length", claimedLength, serializedTransaction.length);
+
+            TransactionData deserializedTransactionData = TransactionTransformer.fromBytes(serializedTransaction);
+            // Re-sign
+            Transaction deserializedTransaction = Transaction.fromData(repository, deserializedTransactionData);
+            deserializedTransaction.sign(signingAccount);
+            assertEquals("Deserialized MESSAGE-type AT transaction signature differs", Base58.encode(transactionData.getSignature()), Base58.encode(deserializedTransactionData.getSignature()));
+
+            // Re-serialize to check new length and bytes
+            final int reclaimedLength = TransactionTransformer.getDataLength(deserializedTransactionData);
+            assertEquals("Reserialized MESSAGE-type AT transaction declared length differs", claimedLength, reclaimedLength);
+
+            byte[] reserializedTransaction = TransactionTransformer.toBytes(deserializedTransactionData);
+            assertEquals("Reserialized MESSAGE-type AT transaction bytes differ", HashCode.fromBytes(serializedTransaction).toString(), HashCode.fromBytes(reserializedTransaction).toString());
+        }
+    }
+
+}
diff --git a/src/test/java/org/qortal/test/common/transaction/AtTestTransaction.java b/src/test/java/org/qortal/test/common/transaction/AtTestTransaction.java
index 38c1c7f3..f827c396 100644
--- a/src/test/java/org/qortal/test/common/transaction/AtTestTransaction.java
+++ b/src/test/java/org/qortal/test/common/transaction/AtTestTransaction.java
@@ -12,15 +12,33 @@ import org.qortal.utils.Amounts;
 public class AtTestTransaction extends TestTransaction {
 
 	public static TransactionData randomTransaction(Repository repository, PrivateKeyAccount account, boolean wantValid) throws DataException {
+		return AtTestTransaction.paymentType(repository, account, wantValid);
+	}
+
+	public static TransactionData paymentType(Repository repository, PrivateKeyAccount account, boolean wantValid) throws DataException {
 		byte[] signature = new byte[64];
 		random.nextBytes(signature);
 		String atAddress = Crypto.toATAddress(signature);
 		String recipient = account.getAddress();
+
+		// Use PAYMENT-type
 		long amount = 123L * Amounts.MULTIPLIER;
 		final long assetId = Asset.QORT;
 
-		// Use PAYMENT-type - i.e. a null message
-		return new ATTransactionData(generateBase(account), atAddress, recipient, amount, assetId, null);
+		return new ATTransactionData(generateBase(account), atAddress, recipient, amount, assetId);
+	}
+
+	public static TransactionData messageType(Repository repository, PrivateKeyAccount account, boolean wantValid) throws DataException {
+		byte[] signature = new byte[64];
+		random.nextBytes(signature);
+		String atAddress = Crypto.toATAddress(signature);
+		String recipient = account.getAddress();
+
+		// Use MESSAGE-type
+		byte[] message = new byte[32];
+		random.nextBytes(message);
+
+		return new ATTransactionData(generateBase(account), atAddress, recipient, message);
 	}
 
 }