diff --git a/eth/sync.go b/eth/sync.go
index 9e180ee200..0ba46e84a5 100644
--- a/eth/sync.go
+++ b/eth/sync.go
@@ -171,6 +171,10 @@ func (pm *ProtocolManager) synchronise(peer *peer) {
 	td := pm.blockchain.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
 
 	pHead, pTd := peer.Head()
+	if pTd := nil {
+		return
+	}
+	
 	if pTd.Cmp(td) <= 0 {
 		return
 	}
@@ -181,10 +185,18 @@ func (pm *ProtocolManager) synchronise(peer *peer) {
 		mode = downloader.FastSync
 	}
 	if mode == downloader.FastSync {
-		// Make sure the peer's total difficulty we are synchronizing is higher.
-		if pm.blockchain.GetTdByHash(pm.blockchain.CurrentFastBlock().Hash()).Cmp(pTd) >= 0 {
-			return
-		}
+		 // Make sure the peer's total difficulty we are synchronizing is higher.
+                fastTd := pm.blockchain.GetTdByHash(pm.blockchain.CurrentFastBlock().Hash())
+                if fastTd == nil {
+                        log.Warn("Fast total difficulty is nil, switch to full sync mode", "hash", pm.blockchain.CurrentFastBlock().Hash().Hex())
+                        //return
+                        mode = downloader.FullSync
+                        atomic.StoreUint32(&pm.fastSync, 0)
+                } else {
+                        if fastTd.Cmp(pTd) >= 0 {
+                                return
+                        }
+                }
 	}
 	// Run the sync cycle, and disable fast sync if we've went past the pivot block
 	if err := pm.downloader.Synchronise(peer.id, pHead, pTd, mode); err != nil {