From 00d1fd0e6fee6cef2565c4a3b2dd428b0d59f4bf Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Sat, 5 Dec 2020 08:01:05 +0900
Subject: Fixed a bug with modules prepended many times.

Adjust insertion point in `fix_prepend_module()`.
---
 src/class.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/class.c b/src/class.c
index a421325a3..7141fe099 100644
--- a/src/class.c
+++ b/src/class.c
@@ -1449,11 +1449,15 @@ fix_prepend_module(mrb_state *mrb, struct RBasic *obj, void *data)
 
   if (c->tt == MRB_TT_CLASS || c->tt == MRB_TT_MODULE) {
     struct RClass *p = c->super;
+    struct RClass *ins_pos = c;
     while (p) {
       if (c == m[0]) break;
+      if (p == m[0]->super->c) {
+        ins_pos = c;
+      }
       if (p->tt == MRB_TT_CLASS) break;
       if (p->c == m[0]) {
-        include_module_at(mrb, c, c, m[1], 0);
+        include_module_at(mrb, ins_pos, ins_pos, m[1], 0);
         break; 
       }
       c = p;
-- 
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