diff --git a/netsync/manager.go b/netsync/manager.go
index fc43d7fbe..31923cc62 100644
--- a/netsync/manager.go
+++ b/netsync/manager.go
@@ -529,8 +529,17 @@ func (sm *SyncManager) handleBlockMsg(bmsg *blockMsg) {
 		return
 	}
 
-	// Request the parents for the orphan block from the peer that sent it.
 	if isOrphan {
+		// If we received an orphan block from the sync peer, it is
+		// misbehaving and must be disconnected from.
+		if peer == sm.syncPeer {
+			log.Errorf("Received an orphan block %s from sync peer %s. Disconnecting...",
+				blockHash, peer)
+			peer.Disconnect()
+			return
+		}
+
+		// Request the parents for the orphan block from the peer that sent it.
 		missingAncestors, err := sm.dag.GetOrphanMissingAncestorHashes(blockHash)
 		if err != nil {
 			log.Errorf("Failed to find missing ancestors for block %s: %s",