diff --git a/src/main/java/org/qortal/transaction/ChatTransaction.java b/src/main/java/org/qortal/transaction/ChatTransaction.java
index ccef1f37..a670ea4b 100644
--- a/src/main/java/org/qortal/transaction/ChatTransaction.java
+++ b/src/main/java/org/qortal/transaction/ChatTransaction.java
@@ -11,6 +11,7 @@ import org.qortal.crypto.MemoryPoW;
 import org.qortal.data.transaction.ChatTransactionData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.group.Group;
+import org.qortal.list.ResourceListManager;
 import org.qortal.repository.DataException;
 import org.qortal.repository.GroupRepository;
 import org.qortal.repository.Repository;
@@ -138,6 +139,12 @@ public class ChatTransaction extends Transaction {
 	public ValidationResult isValid() throws DataException {
 		// Nonce checking is done via isSignatureValid() as that method is only called once per import
 
+		// Check for blacklisted author by address
+		ResourceListManager listManager = ResourceListManager.getInstance();
+		if (listManager.isAddressInBlacklist(this.chatTransactionData.getSender())) {
+			return ValidationResult.ADDRESS_IN_BLACKLIST;
+		}
+
 		// If we exist in the repository then we've been imported as unconfirmed,
 		// but we don't want to make it into a block, so return fake non-OK result.
 		if (this.repository.getTransactionRepository().exists(this.chatTransactionData.getSignature()))
diff --git a/src/main/java/org/qortal/transaction/Transaction.java b/src/main/java/org/qortal/transaction/Transaction.java
index d7dd1455..3c761d28 100644
--- a/src/main/java/org/qortal/transaction/Transaction.java
+++ b/src/main/java/org/qortal/transaction/Transaction.java
@@ -247,6 +247,7 @@ public abstract class Transaction {
 		INVALID_GROUP_BLOCK_DELAY(93),
 		INCORRECT_NONCE(94),
 		INVALID_TIMESTAMP_SIGNATURE(95),
+		ADDRESS_IN_BLACKLIST(96),
 		INVALID_BUT_OK(999),
 		NOT_YET_RELEASED(1000);