diff --git a/example/ck_tile/01_fmha/fmha_bwd_runner.hpp b/example/ck_tile/01_fmha/fmha_bwd_runner.hpp
index f81ae34501..ac86bf4635 100644
--- a/example/ck_tile/01_fmha/fmha_bwd_runner.hpp
+++ b/example/ck_tile/01_fmha/fmha_bwd_runner.hpp
@@ -264,7 +264,7 @@ bwd_result fmha_bwd_run(mode_enum mode,
     ck_tile::HostTensor<LSEDataType> lse_host(
         std::array<ck_tile::index_t, 3>{shape_batch, nhead, shape_seqlen_q});
     ck_tile::HostTensor<LSEDataType> sink_host(
-        sink_grad ? std::array<ck_tile::index_t, 2>{shape_batch, nhead}
+        sink_grad ? std::array<ck_tile::index_t, 2>{batch, nhead}
                   : std::array<ck_tile::index_t, 2>{1, 1} /* dummy when sink is disabled */);
     if(sink_grad)
     {
diff --git a/test/ck_tile/fmha/test_fmha_bwd.cpp b/test/ck_tile/fmha/test_fmha_bwd.cpp
index 3aee76131e..8d90ad9143 100644
--- a/test/ck_tile/fmha/test_fmha_bwd.cpp
+++ b/test/ck_tile/fmha/test_fmha_bwd.cpp
@@ -995,3 +995,83 @@ TEST_P(MultiBatchPadding, DataTypeConfig)
         GTEST_SKIP() << "No instance for multi-batch padding";
     ASSERT_EQ(result, bwd_result::success);
 }
+
+// ============================================================================
+// Regression test for sink_host group-mode OOB fix (PR #7272)
+// ----------------------------------------------------------------------------
+// Bug: in group mode, fmha_bwd_runner.hpp allocated sink_host with first
+// dimension shape_batch (=1) but the fwd reference loop iterates wb in
+// [0, batch-1], causing out-of-bounds reads of heap garbage when batch > 1.
+//
+// Repro condition: sink_grad=true AND mode=group AND batch>=2.
+// Without the fix, the fwd reference computes a poisoned LSE and the bwd
+// validation fails non-deterministically (~25-67% failure rate observed
+// across 30 trial runs at b=2,h=2,s=516,s_k=253,d=72,bf16,mask=no).
+// With the fix (1-line change shape_batch -> batch on line 267 of
+// fmha_bwd_runner.hpp), all 30 runs PASS.
+//
+// This test exercises the fixed code path; a regression that re-introduces
+// the OOB will be detected as flaky/failing validation in CI.
+// ============================================================================
+class SinkGradGroupMode : public TestWithParam<FmhaBwdTestParam>
+{
+};
+INSTANTIATE_TEST_SUITE_P(TestCkTileFmhaBwd,
+                         SinkGradGroupMode,
+                         Combine(Values(mode_enum::group),  // group mode required to hit OOB
+                                 Values(std::tuple{72, -1}, // hdim covered by repro command
+                                        std::tuple{64, -1},
+                                        std::tuple{128, -1}),
+                                 Values(std::tuple{true, true}),  // perm matching repro
+                                 Values("n"),                     // bias=n matching repro
+                                 Values(false),                   // use_dbias
+                                 Values(0.0f),                    // no dropout
+                                 Values(std::tuple{0, 0, false}), // seed/offset/prefs
+                                 Values(std::tuple{2, 2, -1, 516, 253, "0"}, // exact repro config
+                                        std::tuple{2, 2, -1, 516, 253, "1"}, // + causal top-left
+                                        std::tuple{
+                                            2, 2, -1, 516, 253, "2"},      // + causal bottom-right
+                                        std::tuple{3, 4, 2, 259, -1, "0"}, // larger batch, square
+                                        std::tuple{4, 2, -1, 200, 180, "0"}), // batch=4 stress
+                                 Values(false)                                // deterministic
+                                 ));
+TEST_P(SinkGradGroupMode, DataTypeConfig)
+{
+    auto [mode, hdims, perm, bias_str, use_dbias, p_drop, drop_misc, dims_mask, det] = GetParam();
+    auto [hdim_q, hdim_v]                                                            = hdims;
+    auto [i_perm, o_perm]                                                            = perm;
+    auto [drop_seed, drop_offset, drop_prefs]                                        = drop_misc;
+    auto [batch, nhead, nhead_k, seqlen_q, seqlen_k, mask_str]                       = dims_mask;
+
+    auto result = fmha_bwd_run<DataTypeConfig>(
+        mode,
+        batch,
+        nhead,
+        nhead_k,
+        {seqlen_q},
+        {seqlen_k},
+        {-1},
+        {-1},
+        hdim_q,
+        hdim_v,
+        i_perm,
+        o_perm,
+        0, // scale
+        bias_str,
+        use_dbias,
+        p_drop,
+        drop_seed,
+        drop_offset,
+        drop_prefs,
+        mask_str,
+        true, // sink_grad: critical to trigger sink_host alloc/access path
+        det,
+        init_method,
+        static_cast<uint32_t>(ck_tile::EnvValue(CK_TILE_ENV(CK_TILE_TEST_SEED))),
+        1,
+        stream_config);
+
+    if(result == bwd_result::no_instance)
+        GTEST_SKIP() << "No instance for sink_grad group-mode regression";
+    ASSERT_EQ(result, bwd_result::success);
+}