diff --git a/python/sglang/srt/layers/quantization/mxfp4.py b/python/sglang/srt/layers/quantization/mxfp4.py
index 8a0ec4729a69..3c4b3ac12756 100644
--- a/python/sglang/srt/layers/quantization/mxfp4.py
+++ b/python/sglang/srt/layers/quantization/mxfp4.py
@@ -139,8 +139,9 @@ def _swizzle_mxfp4(quant_tensor, scale, num_warps):
     from triton_kernels.tensor_details import layout
 
     if is_sm120_supported():
-        # SM120 (Blackwell desktop) doesn't support persistent kernels / TMA block layout
-        # Use StridedLayout and disable persistent kernels to avoid assertion errors
+        # SM120 desktop Blackwell does not support the persistent/TMA MXFP4 path.
+        # This MXFP4 path uses StridedLayout and the non-persistent kernel with
+        # block_k=128 so the selected tile stays within the per-block shared-memory budget.
         from triton_kernels.tensor_details.layout import StridedLayout
 
         value_layout = StridedLayout
@@ -149,6 +150,7 @@ def _swizzle_mxfp4(quant_tensor, scale, num_warps):
         scale_layout_opts = {}
         constraints = {
             "is_persistent": False,
+            "block_k": 128,
             "num_stages": 1,
         }
         opt_flags.update_opt_flags_constraints(constraints)