diff --git a/csrc/jit_kernels/impls/runtime_utils.hpp b/csrc/jit_kernels/impls/runtime_utils.hpp
index 72a76f0..62f06bd 100644
--- a/csrc/jit_kernels/impls/runtime_utils.hpp
+++ b/csrc/jit_kernels/impls/runtime_utils.hpp
@@ -124,9 +124,9 @@ static CUtensorMap make_tma_2d_desc(const torch::Tensor& t,
         // Inner dim must be a multiple of 64B for .b4x16_p64
         DG_HOST_ASSERT(not fp4_unpacked_smem or gmem_inner_dim % 128 == 0);
 
-        // Fix FP4 packed smem
-        if (not fp4_unpacked_smem and swizzle_mode != 0)
-            smem_inner_dim = swizzle_mode * 2;
+        // For packed FP4 (mxf4nvf4): smem_inner_dim must match the MMA's expected
+        // SMEM row width (BLOCK_K/2 bytes). The default swizzle/elem_size gives the
+        // correct value — do NOT double it. The TMA and MMA must agree on row width.
     }
 
     CUtensorMap tensor_map;