diff --git a/tests/unit/test_d1_debug.py b/tests/unit/test_d1_debug.py
new file mode 100644
index 00000000..4c68a99a
--- /dev/null
+++ b/tests/unit/test_d1_debug.py
@@ -0,0 +1,34 @@
+"""D1: Test hd=64 only with CUDA_LAUNCH_BLOCKING for crash debug."""
+import os
+os.environ['CUDA_LAUNCH_BLOCKING'] = '1'
+import torch, math
+import cutlass.cute as cute
+import cutlass.torch as ct
+import cuda.bindings.driver as cuda
+from dsv4.kernels.attention.fmha import FmhaKernel
+
+hd = 64; n = 128; m = 128
+torch.manual_seed(42)
+q = torch.randn(m, hd, 1, dtype=torch.bfloat16, device='cuda')
+k = torch.randn(n, hd, 1, dtype=torch.bfloat16, device='cuda')
+v = torch.randn(n, hd, dtype=torch.bfloat16, device='cuda')
+c = torch.zeros(m, hd, 1, dtype=torch.bfloat16, device='cuda')
+qf = q[:,:,0].float(); kf = k[:,:,0].float()
+scale = 1.0 / math.sqrt(hd)
+attn = qf @ kf.T * scale; attn = torch.softmax(attn, dim=-1)
+ref = attn @ v.float()
+v_kernel = v.unsqueeze(-1)
+mQ = ct.from_dlpack(q).mark_layout_dynamic(leading_dim=ct.get_leading_dim(q))
+mK = ct.from_dlpack(k).mark_layout_dynamic(leading_dim=ct.get_leading_dim(k))
+mV = ct.from_dlpack(v_kernel).mark_layout_dynamic(leading_dim=ct.get_leading_dim(v_kernel))
+mC = ct.from_dlpack(c).mark_layout_dynamic(leading_dim=ct.get_leading_dim(c))
+stream = cuda.CUstream(torch.cuda.current_stream().cuda_stream)
+kernel = FmhaKernel(head_dim=hd, s_k=n)
+print(f'Compiling hd={hd}...', flush=True)
+compiled = cute.compile(kernel, mQ, mK, mV, mC, stream)
+print(f'Running hd={hd}...', flush=True)
+compiled(mQ, mK, mV, mC, stream)
+torch.cuda.synchronize()
+out = c[:,:,0].float()
+cos = torch.nn.functional.cosine_similarity(out.flatten().unsqueeze(0), ref.flatten().unsqueeze(0)).item()
+print(f'hd={hd}: cos {cos:.6f}')