diff --git a/src/main/java/org/qortal/transaction/BuyNameTransaction.java b/src/main/java/org/qortal/transaction/BuyNameTransaction.java
index 6c390085..370e770a 100644
--- a/src/main/java/org/qortal/transaction/BuyNameTransaction.java
+++ b/src/main/java/org/qortal/transaction/BuyNameTransaction.java
@@ -49,6 +49,15 @@ public class BuyNameTransaction extends Transaction {
 
 	@Override
 	public ValidationResult isValid() throws DataException {
+		Optional<String> buyerPrimaryName = this.getBuyer().getPrimaryName();
+		if( buyerPrimaryName.isPresent()  ) {
+
+			NameData nameData = repository.getNameRepository().fromName(buyerPrimaryName.get());
+			if (nameData.isForSale()) {
+				return ValidationResult.NOT_SUPPORTED;
+			}
+		}
+
 		String name = this.buyNameTransactionData.getName();
 
 		// Check seller address is valid
diff --git a/src/main/java/org/qortal/transaction/SellNameTransaction.java b/src/main/java/org/qortal/transaction/SellNameTransaction.java
index 3b6bf5df..8dcf9bd2 100644
--- a/src/main/java/org/qortal/transaction/SellNameTransaction.java
+++ b/src/main/java/org/qortal/transaction/SellNameTransaction.java
@@ -45,6 +45,12 @@ public class SellNameTransaction extends Transaction {
 	public ValidationResult isValid() throws DataException {
 		String name = this.sellNameTransactionData.getName();
 
+		// if the account has more than one name, then they cannot sell their primary name
+		if( this.repository.getNameRepository().getNamesByOwner(this.getOwner().getAddress()).size() > 1 &&
+				this.getOwner().getPrimaryName().get().equals(name) ) {
+			return ValidationResult.NOT_SUPPORTED;
+		}
+
 		// Check name size bounds
 		int nameLength = Utf8.encodedLength(name);
 		if (nameLength < 1 || nameLength > Name.MAX_NAME_SIZE)
diff --git a/src/test/java/org/qortal/test/naming/BuySellTests.java b/src/test/java/org/qortal/test/naming/BuySellTests.java
index 9788bd7c..6f807265 100644
--- a/src/test/java/org/qortal/test/naming/BuySellTests.java
+++ b/src/test/java/org/qortal/test/naming/BuySellTests.java
@@ -133,6 +133,11 @@ public class BuySellTests extends Common {
 		// check that the order is correct
 		assertEquals(name1, namesByOwner.get(0).getName());
 
+		SellNameTransactionData sellPrimaryNameData = new SellNameTransactionData(TestTransaction.generateBase(alice), name, price);
+		Transaction.ValidationResult sellPrimaryNameResult = TransactionUtils.signAndImport(repository, sellPrimaryNameData, alice);
+
+		// check that selling primary name is not supported while owning multiple addresses
+		assertTrue(Transaction.ValidationResult.NOT_SUPPORTED.equals(sellPrimaryNameResult));
 	}
 
 	@Test
@@ -438,4 +443,60 @@ public class BuySellTests extends Common {
 		assertEquals(bob.getPrimaryName(), bob.determinePrimaryName(TransactionsResource.ConfirmationStatus.CONFIRMED));
 	}
 
+	@Test
+	public void testBuyInvalidationDuringPrimaryNameSale() throws DataException {
+		// mint passed the feature trigger block
+		BlockUtils.mintBlocks(repository, BlockChain.getInstance().getMultipleNamesPerAccountHeight());
+
+		// Register-name
+		testRegisterName();
+
+		// assert primary name for alice
+		Optional<String> alicePrimaryName1 = alice.getPrimaryName();
+		assertTrue(alicePrimaryName1.isPresent());
+		assertTrue(alicePrimaryName1.get().equals(name));
+
+		// Sell-name
+		SellNameTransactionData transactionData = new SellNameTransactionData(TestTransaction.generateBase(alice), name, price);
+		TransactionUtils.signAndMint(repository, transactionData, alice);
+
+		// assert primary name for alice
+		Optional<String> alicePrimaryName2 = alice.getPrimaryName();
+		assertTrue(alicePrimaryName2.isPresent());
+		assertTrue(alicePrimaryName2.get().equals(name));
+
+		NameData nameData;
+
+		// Check name is for sale
+		nameData = repository.getNameRepository().fromName(name);
+		assertTrue(nameData.isForSale());
+		assertEquals("price incorrect", price, nameData.getSalePrice());
+
+		// assert alice cannot register another name while primary name is for sale
+		final String name2 = "another name";
+		RegisterNameTransactionData registerSecondNameData = new RegisterNameTransactionData(TestTransaction.generateBase(alice), name2, "{}");
+		Transaction.ValidationResult registrationResult = TransactionUtils.signAndImport(repository, registerSecondNameData, alice);
+
+		// check that registering is not supported while primary name is for sale
+		assertTrue(Transaction.ValidationResult.NOT_SUPPORTED.equals(registrationResult));
+
+		String bobName = "bob";
+		RegisterNameTransactionData bobRegisterData = new RegisterNameTransactionData(TestTransaction.generateBase(bob), bobName, "{}");
+		transactionData.setFee(new RegisterNameTransaction(null, null).getUnitFee(bobRegisterData.getTimestamp()));
+		TransactionUtils.signAndMint(repository, bobRegisterData, bob);
+
+		Optional<String> bobPrimaryName = bob.getPrimaryName();
+
+		assertTrue(bobPrimaryName.isPresent());
+		assertEquals(bobName, bobPrimaryName.get());
+
+		SellNameTransactionData bobSellData = new SellNameTransactionData(TestTransaction.generateBase(bob), bobName, price);
+		TransactionUtils.signAndMint(repository, bobSellData, bob);
+
+		BuyNameTransactionData aliceBuyData = new BuyNameTransactionData(TestTransaction.generateBase(alice), bobName, price, bob.getAddress());
+		Transaction.ValidationResult aliceBuyResult = TransactionUtils.signAndImport(repository, aliceBuyData, alice);
+
+		// check that buying is not supported while primary name is for sale
+		assertTrue(Transaction.ValidationResult.NOT_SUPPORTED.equals(aliceBuyResult));
+	}
 }