diff --git a/dot/sync/block_queue.go b/dot/sync/block_queue.go
index 57daed89ade..9fc37a459cb 100644
--- a/dot/sync/block_queue.go
+++ b/dot/sync/block_queue.go
@@ -21,7 +21,7 @@ type blockQueue struct {
 func newBlockQueue(capacity int) *blockQueue {
 	return &blockQueue{
 		queue:     make(chan *types.BlockData, capacity),
-		hashesSet: make(map[common.Hash]struct{}),
+		hashesSet: make(map[common.Hash]struct{}, capacity),
 	}
 }