diff --git a/dsv4/kernels/cuda/indexer_fp8_score_topk.cu b/dsv4/kernels/cuda/indexer_fp8_score_topk.cu
index 69975dd2..e2a6f0ae 100644
--- a/dsv4/kernels/cuda/indexer_fp8_score_topk.cu
+++ b/dsv4/kernels/cuda/indexer_fp8_score_topk.cu
@@ -149,8 +149,7 @@ indexer_fp8_score_topk_kernel(
     constexpr int MMA_K_F8 = 32;
     constexpr int NKT = 4;               // ihd=128 / MMA_K_F8=32
     constexpr int TILE_F8 = 128 * 32;    // 4096 bytes per SMEM tile
-    constexpr int TMEM_COLS = 256;  // 128 rows × 128 cols needs 4×128 = 512,
-                                         // but only 64 rows used (2×128 = 256)
+    constexpr int TMEM_COLS = 512;  // 128 rows × 128 cols → 4 row-groups × 128 cols = 512
 
     const int tid = threadIdx.x;
     const int wid = tid >> 5;