From 82609a17e5b4183b9ac0efa8d81ad02e7206f357 Mon Sep 17 00:00:00 2001
From: bbrtj <bbrtj.pro@gmail.com>
Date: Sun, 14 Dec 2025 20:41:28 +0100
Subject: [PATCH 1/2] Fix Perl_av_store off by one error in key comparison

---
 av.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/av.c b/av.c
index 352c1ac03491..3a83fec6ff94 100644
--- a/av.c
+++ b/av.c
@@ -361,7 +361,7 @@ Perl_av_store(pTHX_ AV *av, SSize_t key, SV *val)
             return NULL;
     }
 
-    if (SvREADONLY(av) && key >= AvFILL(av))
+    if (SvREADONLY(av) && key > AvFILL(av))
         croak_no_modify();
 
     if (!AvREAL(av) && AvREIFY(av))

From 32768ce2e49d68b6a9fbc983729390a6e66c4fe9 Mon Sep 17 00:00:00 2001
From: bbrtj <bbrtj.pro@gmail.com>
Date: Tue, 16 Dec 2025 06:23:22 +0100
Subject: [PATCH 2/2] Add a regression test for GH #24006

---
 t/op/array.t | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/t/op/array.t b/t/op/array.t
index cde0ad1251e6..79186b0c6464 100644
--- a/t/op/array.t
+++ b/t/op/array.t
@@ -6,7 +6,7 @@ BEGIN {
     set_up_inc('.', '../lib');
 }
 
-plan (198);
+plan (199);
 
 #
 # @foo, @bar, and @ary are also used from tie-stdarray after tie-ing them
@@ -734,3 +734,15 @@ fresh_perl_is('my @x;$x[0] = 1;shift @x;$x[22] = 1;$x[25] = 1;','',
     is($arr[1], 3,
        'Array element within array range created at correct index from subroutine @_ alias; GH 16364');
 }
+
+# regression test for GH #24006
+{
+    use feature qw(refaliasing);
+    no warnings 'experimental::refaliasing';
+    my @arr = (1, 2);
+    Internals::SvREADONLY(@arr, 1);
+
+    eval { \$arr[1] = \42 };
+    ok !$@, "Last element's contents of a readonly array can be modified";
+}
+