diff --git a/core/blockchain.go b/core/blockchain.go
index 835aac5ee9..a738c73a2e 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -1763,10 +1763,9 @@ func (bc *BlockChain) insertChain(chain types.Blocks, setHead bool) (int, error)
 				throwaway, _ := state.New(parent.Root, bc.stateCache, bc.snaps)
 
 				go func(start time.Time, followup *types.Block, throwaway *state.StateDB) {
-					config := bc.vmConfig
-					config.Tracer = nil
-
-					bc.prefetcher.Prefetch(followup, throwaway, config, &followupInterrupt)
+					vmCfg := bc.vmConfig
+					vmCfg.Tracer = nil
+					bc.prefetcher.Prefetch(followup, throwaway, vmCfg, &followupInterrupt)
 
 					blockPrefetchExecuteTimer.Update(time.Since(start))
 					if followupInterrupt.Load() {