diff --git a/csrc/quantization/cutlass_w8a8/scaled_mm_c3x.cu b/csrc/quantization/cutlass_w8a8/scaled_mm_c3x.cu
index 72d549e597df5..e40f282299685 100644
--- a/csrc/quantization/cutlass_w8a8/scaled_mm_c3x.cu
+++ b/csrc/quantization/cutlass_w8a8/scaled_mm_c3x.cu
@@ -16,29 +16,11 @@ void cutlass_scaled_mm_sm90(torch::Tensor& c, torch::Tensor const& a,
   TORCH_CHECK(a_scales.dtype() == torch::kFloat32);
   TORCH_CHECK(b_scales.dtype() == torch::kFloat32);
 
-  using GroupShape = std::array<int64_t, 2>;
-
   int M = a.size(0), N = b.size(1), K = a.size(1);
 
-  GroupShape a_scale_group_shape = [&, &s = a_scales]() -> GroupShape {
-    if (s.numel() == 1) return {M, K};  // tensor-wise
-    if (s.dim() == 2)
-      return {ceil_div(a.size(0), s.size(0)), ceil_div(a.size(1), s.size(1))};
-    TORCH_CHECK(false, "Unsupported scale shape for scale_a");
-  }();
-
-  GroupShape b_scale_group_shape = [&, &s = b_scales]() -> GroupShape {
-    if (s.numel() == 1) return {K, N};  // tensor-wise
-    if (s.dim() == 2)
-      return {ceil_div(b.size(0), s.size(0)), ceil_div(b.size(1), s.size(1))};
-    TORCH_CHECK(false, "Unsupported scale shape for scale_b");
-  }();
-
-  if ((a_scale_group_shape == GroupShape{M, K} ||
-       a_scale_group_shape == GroupShape{1, K}) &&
-      (b_scale_group_shape == GroupShape{K, N} ||
-       b_scale_group_shape == GroupShape{K, 1})) {
-    // "standard per-tensor/per-token/per-channel" scaling
+  if ((a_scales.numel() == 1 || a_scales.numel() == a.size(0)) &&
+      (b_scales.numel() == 1 || b_scales.numel() == b.size(1))) {
+    // Standard per-tensor/per-token/per-channel scaling
     TORCH_CHECK(a_scales.is_contiguous() && b_scales.is_contiguous());
     if (a.dtype() == torch::kFloat8_e4m3fn) {
       vllm::cutlass_scaled_mm_sm90_fp8(c, a, b, a_scales, b_scales, bias);
@@ -46,25 +28,32 @@ void cutlass_scaled_mm_sm90(torch::Tensor& c, torch::Tensor const& a,
       TORCH_CHECK(a.dtype() == torch::kInt8);
       vllm::cutlass_scaled_mm_sm90_int8(c, a, b, a_scales, b_scales, bias);
     }
-  } else if (a_scale_group_shape == GroupShape{1, 128} &&
-             b_scale_group_shape == GroupShape{128, 128}) {
+  } else {
+    using GroupShape = std::array<int64_t, 2>;
+    auto make_group_shape = [](torch::Tensor const& x,
+                               torch::Tensor const& s) -> GroupShape {
+      TORCH_CHECK(s.dim() == 2, "cutlass_scaled_mm group scales must be 2D");
+      return {ceil_div(x.size(0), s.size(0)), ceil_div(x.size(1), s.size(1))};
+    };
+
+    GroupShape a_scale_group_shape = make_group_shape(a, a_scales);
+    GroupShape b_scale_group_shape = make_group_shape(b, b_scales);
+
     // 1x128 per-token group scales for activations
     // 128x128 blockwise scales for weights
-    TORCH_CHECK(a.dtype() == torch::kFloat8_e4m3fn &&
-                    b.dtype() == torch::kFloat8_e4m3fn,
-                "Currently only FP8 is supported for A group shape 1x128 and "
-                "B group shape 128x128");
-    TORCH_CHECK(!bias, "Bias not yet supported blockwise scaled_mm");
-
-    vllm::cutlass_scaled_mm_blockwise_sm90_fp8(c, a, b, a_scales, b_scales);
-  } else {
-    TORCH_CHECK(false,
-                "Unsupported scale group shapes for CUTLASS 3.x GEMM.\n "
-                "a_scale_group_shape must be [1, 128], got: [",
+    TORCH_CHECK((a_scale_group_shape == GroupShape{1, 128} &&
+                 b_scale_group_shape == GroupShape{128, 128} &&
+                 a.dtype() == torch::kFloat8_e4m3fn &&
+                 b.dtype() == torch::kFloat8_e4m3fn),
+                "cutlass_scaled_mm only supports datatype float8_e4m3fn.\n"
+                "a_scale_group_shape must be [1, 128]. Got: [",
                 a_scale_group_shape[0], ", ", a_scale_group_shape[1],
                 "]\n"
-                "b_scale_group_shape must be [128, 128], got: [",
+                "b_scale_group_shape must be [128, 128]. Got: [",
                 b_scale_group_shape[0], ", ", b_scale_group_shape[1], "]");
+    TORCH_CHECK(!bias, "Bias not yet supported blockwise scaled_mm");
+
+    vllm::cutlass_scaled_mm_blockwise_sm90_fp8(c, a, b, a_scales, b_scales);
   }
 }