diff --git a/consensus/XDPoS/utils/pool.go b/consensus/XDPoS/utils/pool.go
index c2d177a068..399db859e8 100644
--- a/consensus/XDPoS/utils/pool.go
+++ b/consensus/XDPoS/utils/pool.go
@@ -12,6 +12,8 @@ type PoolObj interface {
 	GetSigner() common.Address
 	DeepCopy() interface{}
 }
+
+// Note: must use `NewPool()` to create `Pool` since field `objList` is a map
 type Pool struct {
 	objList map[string]map[common.Hash]PoolObj
 	lock    sync.RWMutex // Protects the pool fields
@@ -22,6 +24,7 @@ func NewPool() *Pool {
 		objList: make(map[string]map[common.Hash]PoolObj),
 	}
 }
+
 func (p *Pool) Get() map[string]map[common.Hash]PoolObj {
 	p.lock.RLock()
 	defer p.lock.RUnlock()