diff --git a/patricia.go b/patricia.go
index 0099e38..a38cae0 100644
--- a/patricia.go
+++ b/patricia.go
@@ -22,8 +22,8 @@ import (
 // patriciaTree is a simple patricia tree that handles []byte instead of string
 // and cannot be changed after instantiation.
 type patriciaTree struct {
-	root *ptNode
-	buf  []byte // preallocated buffer to read data while matching
+	root     *ptNode
+	maxDepth int // max depth of the tree.
 }
 
 func newPatriciaTree(bs ...[]byte) *patriciaTree {
@@ -34,8 +34,8 @@ func newPatriciaTree(bs ...[]byte) *patriciaTree {
 		}
 	}
 	return &patriciaTree{
-		root: newNode(bs),
-		buf:  make([]byte, max+1),
+		root:     newNode(bs),
+		maxDepth: max + 1,
 	}
 }
 
@@ -48,13 +48,15 @@ func newPatriciaTreeString(strs ...string) *patriciaTree {
 }
 
 func (t *patriciaTree) matchPrefix(r io.Reader) bool {
-	n, _ := io.ReadFull(r, t.buf)
-	return t.root.match(t.buf[:n], true)
+	buf := make([]byte, t.maxDepth)
+	n, _ := io.ReadFull(r, buf)
+	return t.root.match(buf[:n], true)
 }
 
 func (t *patriciaTree) match(r io.Reader) bool {
-	n, _ := io.ReadFull(r, t.buf)
-	return t.root.match(t.buf[:n], false)
+	buf := make([]byte, t.maxDepth)
+	n, _ := io.ReadFull(r, buf)
+	return t.root.match(buf[:n], false)
 }
 
 type ptNode struct {