diff --git a/interface.go b/interface.go
index af26fce..cf8afb8 100644
--- a/interface.go
+++ b/interface.go
@@ -52,5 +52,6 @@ type Interface interface {
 	Marshal(io.Writer) error
 
 	ErrorOffset() int
+	Prealloc(uint)
 	Reset()
 }
diff --git a/vector.go b/vector.go
index 977a7ce..98c14ba 100644
--- a/vector.go
+++ b/vector.go
@@ -249,7 +249,8 @@ func (vec *Vector) getNode(depth int) (node *Node, idx int) {
 		node = &vec.nodes[n-1]
 	}
 	vec.nodeL++
-	node.vptr, node.depth = vec.ptr(), depth
+	node.depth = depth
+	node.vptr = vec.ptr()
 	node.key.vptr, node.val.vptr = node.vptr, node.vptr
 	idx = vec.Len() - 1
 	node.idx = idx
@@ -275,6 +276,13 @@ func (vec *Vector) ErrorOffset() int {
 	return vec.errOff
 }
 
+// Prealloc prepares space for further parse.
+func (vec *Vector) Prealloc(size uint) {
+	if ul := uint(len(vec.nodes)); ul < size {
+		vec.nodes = append(vec.nodes, make([]Node, size-ul+1)...)
+	}
+}
+
 // Reset vector data.
 func (vec *Vector) Reset() {
 	if vec.nodeL == 0 {