diff --git a/core/state/trie_prefetcher.go b/core/state/trie_prefetcher.go
index 21c9f1a27f..cdc03c606f 100644
--- a/core/state/trie_prefetcher.go
+++ b/core/state/trie_prefetcher.go
@@ -245,7 +245,10 @@ func (sf *subfetcher) schedule(keys [][]byte) {
 	sf.tasks = append(sf.tasks, keys...)
 	sf.lock.Unlock()
 	// Notify the prefetcher. The wake-chan is buffered, so this is async.
-	sf.wake <- true
+	select {
+	case sf.wake <- true:
+	default:
+	}
 }
 
 // wait waits for the subfetcher to finish it's task. It is safe to call wait multiple
diff --git a/miner/worker.go b/miner/worker.go
index a642d46b6f..f680702814 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -125,7 +125,7 @@ func (env *environment) discard() {
 	if env.state == nil {
 		return
 	}
-	//env.state.StopPrefetcher()
+	env.state.StopPrefetcher()
 }
 
 // task contains all information for consensus engine sealing and result submitting.
@@ -711,7 +711,7 @@ func (w *worker) makeEnv(parent *types.Header, header *types.Header, coinbase co
 	if err != nil {
 		return nil, err
 	}
-	//state.StartPrefetcher("miner")
+	state.StartPrefetcher("miner")
 
 	// Note the passed coinbase may be different with header.Coinbase.
 	env := &environment{