diff --git a/mpc.c b/mpc.c
index e5c350e..6c65255 100644
--- a/mpc.c
+++ b/mpc.c
@@ -2776,11 +2776,11 @@ void mpc_ast_print_to(mpc_ast_t *a, FILE *fp) {
   mpc_ast_print_depth(a, 0, fp);
 }
 
-int mpc_ast_get_index(mpc_ast_t *ast, char *tag) {
+int mpc_ast_get_index(mpc_ast_t *ast, const char *tag) {
     return mpc_ast_get_index_lb(ast, tag, 0);
 }
 
-int mpc_ast_get_index_lb(mpc_ast_t *ast, char *tag, int lb) {
+int mpc_ast_get_index_lb(mpc_ast_t *ast, const char *tag, int lb) {
     int i;
 
     for(i=lb; i<ast->children_num; i++) {
@@ -2792,11 +2792,11 @@ int mpc_ast_get_index_lb(mpc_ast_t *ast, char *tag, int lb) {
     return -1;
 }
 
-mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, char *tag) {
+mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, const char *tag) {
     return mpc_ast_get_child_lb(ast, tag, 0);
 }
 
-mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, char *tag, int lb) {
+mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, const char *tag, int lb) {
     int i;
 
     for(i=lb; i<ast->children_num; i++) {
diff --git a/mpc.h b/mpc.h
index 02a6b4e..82ee6ba 100644
--- a/mpc.h
+++ b/mpc.h
@@ -276,10 +276,10 @@ void mpc_ast_delete(mpc_ast_t *a);
 void mpc_ast_print(mpc_ast_t *a);
 void mpc_ast_print_to(mpc_ast_t *a, FILE *fp);
 
-int mpc_ast_get_index(mpc_ast_t *ast, char *tag);
-int mpc_ast_get_index_lb(mpc_ast_t *ast, char *tag, int lb);
-mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, char *tag);
-mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, char *tag, int lb);
+int mpc_ast_get_index(mpc_ast_t *ast, const char *tag);
+int mpc_ast_get_index_lb(mpc_ast_t *ast, const char *tag, int lb);
+mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, const char *tag);
+mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, const char *tag, int lb);
 
 /*
 ** Warning: This function currently doesn't test for equality of the `state` member!