diff --git a/dsv4/kernels/router/nvfp4_fused_router_kernel.py b/dsv4/kernels/router/nvfp4_fused_router_kernel.py
index 2cd47635..6f945207 100644
--- a/dsv4/kernels/router/nvfp4_fused_router_kernel.py
+++ b/dsv4/kernels/router/nvfp4_fused_router_kernel.py
@@ -125,15 +125,15 @@ class Nvfp4FusedRouterKernel:
         self._tiled_mma = tiled_mma
         self._tiled_mma_sfb = tiled_mma_sfb
 
-        mma_inst_shape_k = cute.size(tiled_mma.shape_mnk, mode=[2])
+        mma_inst_shape_k = 32  # NVFP4 sf_vec_size=16: MMA inst K = sf_vec_size * 2 (FP4 packing)
         mma_inst_tile_k = 4
         self.mma_tiler = (
             self.mma_inst_shape_mn[0], self.mma_inst_shape_mn[1],
-            mma_inst_shape_k * mma_inst_tile_k,
+            cutlass.Int32(mma_inst_shape_k * mma_inst_tile_k),
         )
         self.mma_tiler_sfb = (
             self.mma_inst_shape_mn_sfb[0], self.mma_inst_shape_mn_sfb[1],
-            mma_inst_shape_k * mma_inst_tile_k,
+            cutlass.Int32(mma_inst_shape_k * mma_inst_tile_k),
         )
         self.cta_tile_shape_mnk = (
             self.mma_tiler[0] // cute.size(tiled_mma.thr_id.shape),