From a06adb176f3c0d44b15ff41fa7788ae408147df2 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby-lang.org>
Date: Fri, 18 Aug 2017 23:40:27 +0900
Subject: `mrb_str_cat`: `capa` should be bigger than `total`.

---
 src/string.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/string.c b/src/string.c
index c5efd779f..e382b470c 100644
--- a/src/string.c
+++ b/src/string.c
@@ -2566,15 +2566,15 @@ mrb_str_cat(mrb_state *mrb, mrb_value str, const char *ptr, size_t len)
     mrb_raise(mrb, E_ARGUMENT_ERROR, "string size too big");
   }
   if (capa <= total) {
-    while (total > capa) {
+    while (capa <= total) {
       if (capa <= MRB_INT_MAX / 2) {
         capa *= 2;
       }
       else {
-        capa = total;
+        capa = total+1;
       }
     }
-    if (capa < total || capa > MRB_INT_MAX) {
+    if (capa <= total || capa > MRB_INT_MAX) {
       goto size_error;
     }
     resize_capa(mrb, s, capa);
-- 
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