diff --git a/include/r3_str.h b/include/r3_str.h
index 2a4d5a5..371451c 100644
--- a/include/r3_str.h
+++ b/include/r3_str.h
@@ -14,13 +14,13 @@ int slug_count(const char * p, int len);
 
 char * slug_compile(char * str, int len);
 
-bool contains_slug(char * str);
+bool contains_slug(const char * str);
 
 char * slug_find_pattern(char *s1, int *len);
 
 char * slug_find_placeholder(char *s1, int *len);
 
-char * inside_slug(char * needle, int needle_len, char *offset);
+char * inside_slug(const char * needle, int needle_len, char *offset);
 
 char * ltrim_slash(char* str);
 
diff --git a/src/node.c b/src/node.c
index 297251b..e3cf031 100644
--- a/src/node.c
+++ b/src/node.c
@@ -480,7 +480,7 @@ node * r3_tree_insert_pathl_(node *tree, char *path, int path_len, route * route
     /* length of common prefix */
     int prefix_len = 0;
     for( int i = 0 ; i < n->edge_len ; i++ ) {
-        prefix_len = strndiff( path, n->edges[i]->pattern, n->edges[i]->pattern_len);
+        prefix_len = strndiff( (char*) path, n->edges[i]->pattern, n->edges[i]->pattern_len);
 
         // printf("prefix_len: %d   %s vs %s\n", prefix_len, path, n->edges[i]->pattern );
 
diff --git a/src/str.c b/src/str.c
index ffc3fe7..bcd6540 100644
--- a/src/str.c
+++ b/src/str.c
@@ -59,11 +59,11 @@ int slug_count(const char * p, int len) {
     return s;
 }
 
-bool contains_slug(char * str) {
+bool contains_slug(const char * str) {
     return strchr(str, '{') != NULL ? TRUE : FALSE;
 }
 
-char * inside_slug(char * needle, int needle_len, char *offset) {
+char * inside_slug(const char * needle, int needle_len, char *offset) {
     char * s1 = offset;
     char * s2 = offset;