diff --git a/include/r3.h b/include/r3.h
index 14ec6ba..e4583f3 100644
--- a/include/r3.h
+++ b/include/r3.h
@@ -124,14 +124,14 @@ int r3_tree_render_file(node * tree, char * format, char * filename);
 
 int r3_tree_render_dot(node * tree);
 
-edge * r3_node_find_edge_str(node * n, char * str, int str_len);
+edge * r3_node_find_edge_str(const node * n, char * str, int str_len);
 
 
 void r3_tree_compile(node *n);
 
 void r3_tree_compile_patterns(node * n);
 
-node * r3_tree_matchl(node * n, char * path, int path_len, match_entry * entry);
+node * r3_tree_matchl(const node * n, char * path, int path_len, match_entry * entry);
 
 #define r3_tree_match(n,p,e)  r3_tree_matchl(n,p, strlen(p), e)
 
@@ -165,7 +165,7 @@ void r3_node_append_route(node * n, route * route);
 
 void r3_route_free(route * route);
 
-route * r3_tree_match_route(node *n, match_entry * entry);
+route * r3_tree_match_route(const node *n, match_entry * entry);
 
 #define METHOD_GET 2
 #define METHOD_POST 2<<1
diff --git a/src/node.c b/src/node.c
index 7085e29..9741e40 100644
--- a/src/node.c
+++ b/src/node.c
@@ -252,7 +252,7 @@ void match_entry_free(match_entry * entry) {
  * @param int          path_len the length of the URL path.
  * @param match_entry* entry match_entry is used for saving the captured dynamic strings from pcre result.
  */
-node * r3_tree_matchl(node * n, char * path, int path_len, match_entry * entry) {
+node * r3_tree_matchl(const node * n, char * path, int path_len, match_entry * entry) {
     info("try matching: %s\n", path);
 
     edge *e;
@@ -328,7 +328,7 @@ node * r3_tree_matchl(node * n, char * path, int path_len, match_entry * entry)
     return NULL;
 }
 
-route * r3_tree_match_route(node *tree, match_entry * entry) {
+route * r3_tree_match_route(const node *tree, match_entry * entry) {
     node *n;
     n = r3_tree_match_entry(tree, entry);
     if (n->routes && n->route_len > 0) {
@@ -342,7 +342,7 @@ route * r3_tree_match_route(node *tree, match_entry * entry) {
     return NULL;
 }
 
-inline edge * r3_node_find_edge_str(node * n, char * str, int str_len) {
+inline edge * r3_node_find_edge_str(const node * n, char * str, int str_len) {
     int i = 0;
     int matched_idx = 0;
     char firstbyte = *str;
diff --git a/tests/bench_str.csv b/tests/bench_str.csv
index 40dc980..1b3d4f7 100644
--- a/tests/bench_str.csv
+++ b/tests/bench_str.csv
@@ -428,3 +428,7 @@
 1400606406,13923000.83
 1400606409,13742645.62
 1400606411,13878225.03
+1400606451,13922301.44
+1400606491,14030387.83
+1400606523,13157029.51
+1400606567,13999364.95