diff --git a/src/nvfp4_megamoe_kernel/nvfp4_mega_moe.py b/src/nvfp4_megamoe_kernel/nvfp4_mega_moe.py
index 63289236..95cb1dee 100644
--- a/src/nvfp4_megamoe_kernel/nvfp4_mega_moe.py
+++ b/src/nvfp4_megamoe_kernel/nvfp4_mega_moe.py
@@ -109,6 +109,8 @@ def _prepack_weight_sf(weight_sf, N, K, tag):
     if cache_key in _prepack_weight_sf._cache:
         return _prepack_weight_sf._cache[cache_key]
 
+    assert weight_sf.dtype == torch.float8_e4m3fn, weight_sf.dtype
+
     from nvfp4_megamoe_kernel.cutlass_nvfp4_gemm.kernel import prepack_sfb
 
     E = weight_sf.shape[0]