diff --git a/src/main/java/org/qortal/controller/Controller.java b/src/main/java/org/qortal/controller/Controller.java
index 0c9e30f6..0026be41 100644
--- a/src/main/java/org/qortal/controller/Controller.java
+++ b/src/main/java/org/qortal/controller/Controller.java
@@ -830,6 +830,10 @@ public class Controller extends Thread {
 		}
 	}
 
+	private void removeIncomingTransaction(byte[] signature) {
+		incomingTransactions.removeIf(t -> Arrays.equals(t.getSignature(), signature));
+	}
+
 	private void processIncomingTransactionsQueue() {
 		if (this.incomingTransactions.size() == 0) {
 			// Don't bother locking if there are no new transactions to process
@@ -853,70 +857,73 @@ public class Controller extends Thread {
 		}
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
+			LOGGER.debug("Processing incoming transactions queue (size {})...", this.incomingTransactions.size());
+
+			// Take a copy of incomingTransactions so we can release the lock
+			List<TransactionData>incomingTransactionsCopy = new ArrayList<>(this.incomingTransactions);
 
 			// Iterate through incoming transactions list
-			synchronized (this.incomingTransactions) { // Required in order to safely iterate a synchronizedList()
-				Iterator iterator = this.incomingTransactions.iterator();
-				while (iterator.hasNext()) {
-					if (isStopping) {
-						return;
-					}
+			Iterator iterator = incomingTransactionsCopy.iterator();
+			while (iterator.hasNext()) {
+				if (isStopping) {
+					return;
+				}
 
-					if (Synchronizer.getInstance().isSyncRequestPending()) {
-						LOGGER.debug("Breaking out of transaction processing loop with {} remaining, because a sync request is pending", this.incomingTransactions.size());
-						return;
-					}
+				if (Synchronizer.getInstance().isSyncRequestPending()) {
+					LOGGER.debug("Breaking out of transaction processing loop with {} remaining, because a sync request is pending", incomingTransactionsCopy.size());
+					return;
+				}
 
-					TransactionData transactionData = (TransactionData) iterator.next();
-					Transaction transaction = Transaction.fromData(repository, transactionData);
+				TransactionData transactionData = (TransactionData) iterator.next();
+				Transaction transaction = Transaction.fromData(repository, transactionData);
 
-					// Check signature
-					if (!transaction.isSignatureValid()) {
-						LOGGER.trace(() -> String.format("Ignoring %s transaction %s with invalid signature", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
-						iterator.remove();
-						continue;
-					}
+				// Check signature
+				if (!transaction.isSignatureValid()) {
+					LOGGER.trace(() -> String.format("Ignoring %s transaction %s with invalid signature", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
+					removeIncomingTransaction(transactionData.getSignature());
+					continue;
+				}
 
-					ValidationResult validationResult = transaction.importAsUnconfirmed();
+				ValidationResult validationResult = transaction.importAsUnconfirmed();
 
-					if (validationResult == ValidationResult.TRANSACTION_ALREADY_EXISTS) {
-						LOGGER.trace(() -> String.format("Ignoring existing transaction %s", Base58.encode(transactionData.getSignature())));
-						iterator.remove();
-						continue;
-					}
+				if (validationResult == ValidationResult.TRANSACTION_ALREADY_EXISTS) {
+					LOGGER.trace(() -> String.format("Ignoring existing transaction %s", Base58.encode(transactionData.getSignature())));
+					removeIncomingTransaction(transactionData.getSignature());
+					continue;
+				}
 
-					if (validationResult == ValidationResult.NO_BLOCKCHAIN_LOCK) {
-						LOGGER.trace(() -> String.format("Couldn't lock blockchain to import unconfirmed transaction", Base58.encode(transactionData.getSignature())));
-						iterator.remove();
-						continue;
-					}
+				if (validationResult == ValidationResult.NO_BLOCKCHAIN_LOCK) {
+					LOGGER.trace(() -> String.format("Couldn't lock blockchain to import unconfirmed transaction", Base58.encode(transactionData.getSignature())));
+					removeIncomingTransaction(transactionData.getSignature());
+					continue;
+				}
 
-					if (validationResult != ValidationResult.OK) {
-						final String signature58 = Base58.encode(transactionData.getSignature());
-						LOGGER.trace(() -> String.format("Ignoring invalid (%s) %s transaction %s", validationResult.name(), transactionData.getType().name(), signature58));
-						Long now = NTP.getTime();
-						if (now != null && now - transactionData.getTimestamp() > INVALID_TRANSACTION_STALE_TIMEOUT) {
-							Long expiryLength = INVALID_TRANSACTION_RECHECK_INTERVAL;
-							if (validationResult == ValidationResult.TIMESTAMP_TOO_OLD) {
-								// Use shorter recheck interval for expired transactions
-								expiryLength = EXPIRED_TRANSACTION_RECHECK_INTERVAL;
-							}
-							Long expiry = now + expiryLength;
-							LOGGER.debug("Adding stale invalid transaction {} to invalidUnconfirmedTransactions...", signature58);
-							// Invalid, unconfirmed transaction has become stale - add to invalidUnconfirmedTransactions so that we don't keep requesting it
-							invalidUnconfirmedTransactions.put(signature58, expiry);
+				if (validationResult != ValidationResult.OK) {
+					final String signature58 = Base58.encode(transactionData.getSignature());
+					LOGGER.trace(() -> String.format("Ignoring invalid (%s) %s transaction %s", validationResult.name(), transactionData.getType().name(), signature58));
+					Long now = NTP.getTime();
+					if (now != null && now - transactionData.getTimestamp() > INVALID_TRANSACTION_STALE_TIMEOUT) {
+						Long expiryLength = INVALID_TRANSACTION_RECHECK_INTERVAL;
+						if (validationResult == ValidationResult.TIMESTAMP_TOO_OLD) {
+							// Use shorter recheck interval for expired transactions
+							expiryLength = EXPIRED_TRANSACTION_RECHECK_INTERVAL;
 						}
-						iterator.remove();
-						continue;
+						Long expiry = now + expiryLength;
+						LOGGER.debug("Adding stale invalid transaction {} to invalidUnconfirmedTransactions...", signature58);
+						// Invalid, unconfirmed transaction has become stale - add to invalidUnconfirmedTransactions so that we don't keep requesting it
+						invalidUnconfirmedTransactions.put(signature58, expiry);
 					}
-
-					LOGGER.debug(() -> String.format("Imported %s transaction %s", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
-					iterator.remove();
+					removeIncomingTransaction(transactionData.getSignature());
+					continue;
 				}
+
+				LOGGER.debug(() -> String.format("Imported %s transaction %s", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
+				removeIncomingTransaction(transactionData.getSignature());
 			}
 		} catch (DataException e) {
 			LOGGER.error(String.format("Repository issue while processing incoming transactions", e));
 		} finally {
+			LOGGER.debug("Finished processing incoming transactions queue");
 			blockchainLock.unlock();
 		}
 	}