diff --git a/include/mruby.h b/include/mruby.h
index 28eea6929..ee73defb9 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -227,7 +227,7 @@ void *mrb_malloc(mrb_state*, size_t);
 void *mrb_calloc(mrb_state*, size_t, size_t);
 void *mrb_realloc(mrb_state*, void*, size_t);
 struct RBasic *mrb_obj_alloc(mrb_state*, enum mrb_vtype, struct RClass*);
-void *mrb_free(mrb_state*, void*);
+void mrb_free(mrb_state*, void*);
 
 mrb_value mrb_str_new(mrb_state *mrb, const char *p, size_t len);
 mrb_value mrb_str_new_cstr(mrb_state*, const char*);
diff --git a/src/gc.c b/src/gc.c
index 19354b301..b6493b859 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -197,10 +197,10 @@ mrb_calloc(mrb_state *mrb, size_t nelem, size_t len)
   return p;
 }
 
-void*
+void
 mrb_free(mrb_state *mrb, void *p)
 {
-  return (mrb->allocf)(mrb, p, 0, mrb->ud);
+  (mrb->allocf)(mrb, p, 0, mrb->ud);
 }
 
 #ifndef MRB_HEAP_PAGE_SIZE