diff --git a/gc.c b/gc.c
index 92d78f036ea01e..b850d4a79ad039 100644
--- a/gc.c
+++ b/gc.c
@@ -3905,7 +3905,7 @@ should_be_finalizable(VALUE obj)
     rb_check_frozen(obj);
 }
 
-VALUE
+static VALUE
 rb_define_finalizer_no_check(VALUE obj, VALUE block)
 {
     rb_objspace_t *objspace = &rb_objspace;
diff --git a/internal/gc.h b/internal/gc.h
index b11f1775fba872..c4157b51bcac58 100644
--- a/internal/gc.h
+++ b/internal/gc.h
@@ -242,7 +242,6 @@ size_t rb_gc_obj_slot_size(VALUE obj);
 bool rb_gc_size_allocatable_p(size_t size);
 int rb_objspace_garbage_object_p(VALUE obj);
 bool rb_gc_is_ptr_to_obj(const void *ptr);
-VALUE rb_define_finalizer_no_check(VALUE obj, VALUE block);
 
 void rb_gc_mark_and_move(VALUE *ptr);