diff --git a/include/cfunc.h b/include/cfunc.h
index 8f525e5..39587bc 100644
--- a/include/cfunc.h
+++ b/include/cfunc.h
@@ -58,9 +58,9 @@ static inline struct cfunc_state *
 cfunc_state(mrb_state *mrb, struct RClass* obj)
 {
     if(obj == NULL) {
-        obj = (struct RClass*) mrb_object(mrb_vm_const_get(mrb, mrb_intern(mrb, "CFunc")));
+        obj = (struct RClass*) mrb_object(mrb_vm_const_get(mrb, mrb_intern_cstr(mrb, "CFunc")));
     }
-    mrb_value state = mrb_mod_cv_get(mrb, obj, mrb_intern(mrb, "cfunc_state"));
+    mrb_value state = mrb_mod_cv_get(mrb, obj, mrb_intern_cstr(mrb, "cfunc_state"));
     return (struct cfunc_state *)mrb_voidp(state);
 }
 
@@ -69,7 +69,7 @@ static inline void
 set_cfunc_state(mrb_state *mrb, struct RClass* klass, struct cfunc_state *state)
 {
     mrb_value mstate = mrb_voidp_value(mrb, state);
-    mrb_mod_cv_set(mrb, klass, mrb_intern(mrb, "cfunc_state"), mstate);
+    mrb_mod_cv_set(mrb, klass, mrb_intern_cstr(mrb, "cfunc_state"), mstate);
 }
 
 #endif