diff --git a/gc/gc_impl.h b/gc/gc_impl.h
index a68b2a7932..ab21e4e81b 100644
--- a/gc/gc_impl.h
+++ b/gc/gc_impl.h
@@ -1,5 +1,5 @@
-#ifndef GC_IMPL_H
-#define GC_IMPL_H
+#ifndef GC_GC_IMPL_H
+#define GC_GC_IMPL_H
 
 #include "ruby/ruby.h"