diff --git a/trie/secure_trie.go b/trie/secure_trie.go
index e38d5ac4dc..6297f6f294 100644
--- a/trie/secure_trie.go
+++ b/trie/secure_trie.go
@@ -224,7 +224,7 @@ func (t *StateTrie) GetKey(shaKey []byte) []byte {
 func (t *StateTrie) Commit(collectLeaf bool) (common.Hash, *trienode.NodeSet, error) {
 	// Write all the pre-images to the actual disk database
 	if len(t.getSecKeyCache()) > 0 {
-		preimages := make(map[common.Hash][]byte)
+		preimages := make(map[common.Hash][]byte, len(t.secKeyCache))
 		for hk, key := range t.secKeyCache {
 			preimages[common.BytesToHash([]byte(hk))] = key
 		}
diff --git a/trie/trienode/node.go b/trie/trienode/node.go
index aa8a0f6d99..fa7bebe4f9 100644
--- a/trie/trienode/node.go
+++ b/trie/trienode/node.go
@@ -186,7 +186,7 @@ func (set *MergedNodeSet) Merge(other *NodeSet) error {
 
 // Flatten returns a two-dimensional map for internal nodes.
 func (set *MergedNodeSet) Flatten() map[common.Hash]map[string]*Node {
-	nodes := make(map[common.Hash]map[string]*Node)
+	nodes := make(map[common.Hash]map[string]*Node, len(set.Sets))
 	for owner, set := range set.Sets {
 		nodes[owner] = set.Nodes
 	}