diff --git a/src/main/java/org/qortal/controller/Synchronizer.java b/src/main/java/org/qortal/controller/Synchronizer.java
index 97d70027..f8ea0ec0 100644
--- a/src/main/java/org/qortal/controller/Synchronizer.java
+++ b/src/main/java/org/qortal/controller/Synchronizer.java
@@ -343,7 +343,7 @@ public class Synchronizer {
 						}
 
 						// Ignore this peer if it holds an invalid block
-						if (this.containsInvalidBlock(peer.getCommonBlockData().getBlockSummariesAfterCommonBlock())) {
+						if (this.containsInvalidBlockSummary(peer.getCommonBlockData().getBlockSummariesAfterCommonBlock())) {
 							LOGGER.debug("Ignoring peer %s because it holds an invalid block", peer);
 							peers.remove(peer);
 						}
@@ -503,7 +503,7 @@ public class Synchronizer {
 		}
 		invalidBlockSignatures.add(signature);
 	}
-	private boolean containsInvalidBlock(List<BlockSummaryData> blockSummaries) {
+	private boolean containsInvalidBlockSummary(List<BlockSummaryData> blockSummaries) {
 		if (blockSummaries == null || invalidBlockSignatures == null) {
 			return false;
 		}
@@ -519,6 +519,21 @@ public class Synchronizer {
 		}
 		return false;
 	}
+	private boolean containsInvalidBlockSignature(List<byte[]> blockSignatures) {
+		if (blockSignatures == null || invalidBlockSignatures == null) {
+			return false;
+		}
+
+		//  Loop through supplied block signatures and check each one against our known invalid blocks
+		for (byte[] signature : blockSignatures) {
+			for (byte[] invalidSignature : invalidBlockSignatures) {
+				if (Arrays.equals(signature, invalidSignature)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
 
 
 	/**
@@ -920,6 +935,12 @@ public class Synchronizer {
 				break;
 			}
 
+			// Catch a block with an invalid signature before orphaning, so that we retain our existing valid candidate
+			if (this.containsInvalidBlockSignature(peerBlockSignatures)) {
+				LOGGER.info(String.format("Peer %s sent invalid block signature: %.8s", peer, Base58.encode(latestPeerSignature)));
+				return SynchronizationResult.INVALID_DATA;
+			}
+
 			byte[] nextPeerSignature = peerBlockSignatures.get(0);
 			int nextHeight = height + 1;