diff --git a/consensus/istanbul/core/core.go b/consensus/istanbul/core/core.go
index 76884d6c43..c4fd5501b9 100644
--- a/consensus/istanbul/core/core.go
+++ b/consensus/istanbul/core/core.go
@@ -166,7 +166,7 @@ func (c *core) IsProposer() bool {
 }
 
 func (c *core) IsCurrentProposal(blockHash common.Hash) bool {
-	return c.current.pendingRequest != nil && c.current.pendingRequest.Proposal.Hash() == blockHash
+	return c.current != nil && c.current.pendingRequest != nil && c.current.pendingRequest.Proposal.Hash() == blockHash
 }
 
 func (c *core) commit() {
diff --git a/miner/worker.go b/miner/worker.go
index 0d2eb420a1..93b897d269 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -605,7 +605,9 @@ func (w *worker) resultLoop() {
 			allReceipts := mergeReceipts(work.receipts, work.privateReceipts)
 
 			// Commit block and state to database.
+			w.mu.Lock()
 			stat, err := w.chain.WriteBlockWithState(block, allReceipts, work.state, nil)
+			w.mu.Unlock()
 			if err != nil {
 				log.Error("Failed writWriteBlockAndStating block to chain", "err", err)
 				continue