From 8b02fe6178427b96aea25396b53ea4ae8cadd7d8 Mon Sep 17 00:00:00 2001
From: Grzegorz Owsiany <gowsiany@users.noreply.github.com>
Date: Thu, 27 Nov 2025 03:12:24 +0100
Subject: [PATCH] [C++] Fix vtable deduplication for 64-bit buffers >2GB
 (#8591)

Fixes #8590
---
 include/flatbuffers/flatbuffer_builder.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/flatbuffers/flatbuffer_builder.h b/include/flatbuffers/flatbuffer_builder.h
index 8d221f6e6..5522de361 100644
--- a/include/flatbuffers/flatbuffer_builder.h
+++ b/include/flatbuffers/flatbuffer_builder.h
@@ -469,8 +469,8 @@ class FlatBufferBuilderImpl {
     if (dedup_vtables_) {
       for (auto it = buf_.scratch_data(); it < buf_.scratch_end();
            it += sizeof(uoffset_t)) {
-        auto vt_offset_ptr = reinterpret_cast<uoffset_t*>(it);
-        auto vt2 = reinterpret_cast<voffset_t*>(buf_.data_at(*vt_offset_ptr));
+        auto vt_offset_ptr = reinterpret_cast<uoffset_t *>(it);
+        auto vt2 = reinterpret_cast<voffset_t *>(buf_.data_at(*vt_offset_ptr + length_of_64_bit_region_));
         auto vt2_size = ReadScalar<voffset_t>(vt2);
         if (vt1_size != vt2_size || 0 != memcmp(vt2, vt1, vt1_size)) continue;
         vt_use = *vt_offset_ptr;