diff --git a/src/main/java/org/qortal/controller/Controller.java b/src/main/java/org/qortal/controller/Controller.java
index cde965c1..7ce94b1e 100644
--- a/src/main/java/org/qortal/controller/Controller.java
+++ b/src/main/java/org/qortal/controller/Controller.java
@@ -722,6 +722,43 @@ public class Controller extends Thread {
 		return lastMisbehaved != null && lastMisbehaved > NTP.getTime() - MISBEHAVIOUR_COOLOFF;
 	};
 
+	public static final Predicate<Peer> hasInvalidBlock = peer -> {
+		final PeerChainTipData peerChainTipData = peer.getChainTipData();
+		Map<String, Long> invalidBlockSignatures = Synchronizer.getInstance().getInvalidBlockSignatures();
+		List<byte[]> peerSignatures = new ArrayList<>();
+
+		// Add peer's latest block signature
+		if (peerChainTipData != null) {
+			peerSignatures.add(peerChainTipData.getLastBlockSignature());
+		}
+
+		// Add peer's blocks since common block
+		if (peer.getCommonBlockData() == null) {
+			List<BlockSummaryData> peerSummaries = peer.getCommonBlockData().getBlockSummariesAfterCommonBlock();
+			if (peerSummaries != null) {
+				for (BlockSummaryData blockSummaryData : peerSummaries) {
+					peerSignatures.add(blockSummaryData.getSignature());
+				}
+			}
+		}
+
+		// Shortcut if no data
+		if (peerSignatures.isEmpty() || invalidBlockSignatures == null || invalidBlockSignatures.isEmpty()) {
+			return false;
+		}
+
+		// Loop through our known invalid blocks and check each one against supplied block summaries
+		for (String invalidSignature58 : invalidBlockSignatures.keySet()) {
+			byte[] invalidSignature = Base58.decode(invalidSignature58);
+			for (byte[] peerSignature : peerSignatures) {
+				if (Arrays.equals(peerSignature, invalidSignature)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	};
+
 	public static final Predicate<Peer> hasNoRecentBlock = peer -> {
 		final Long minLatestBlockTimestamp = getMinimumLatestBlockTimestamp();
 		final PeerChainTipData peerChainTipData = peer.getChainTipData();
diff --git a/src/main/java/org/qortal/controller/Synchronizer.java b/src/main/java/org/qortal/controller/Synchronizer.java
index 597752d2..e1f248dd 100644
--- a/src/main/java/org/qortal/controller/Synchronizer.java
+++ b/src/main/java/org/qortal/controller/Synchronizer.java
@@ -241,6 +241,10 @@ public class Synchronizer extends Thread {
 		// Compare the peers against each other, and against our chain, which will return an updated list excluding those without common blocks
 		peers = Synchronizer.getInstance().comparePeers(peers);
 
+		// Disregard peers that hold invalid blocks
+		// Make sure this is after findCommonBlocksWithPeers() so that peers' summaries can be updated
+		peers.removeIf(Controller.hasInvalidBlock);
+
 		// We may have added more inferior chain tips when comparing peers, so remove any peers that are currently on those chains
 		peers.removeIf(Controller.hasInferiorChainTip);
 
@@ -840,6 +844,10 @@ public class Synchronizer extends Thread {
 
 	/* Invalid block signature tracking */
 
+	public Map<String, Long> getInvalidBlockSignatures() {
+		return this.invalidBlockSignatures;
+	}
+
 	private void addInvalidBlockSignature(byte[] signature) {
 		Long now = NTP.getTime();
 		if (now == null) {