diff --git a/src/test_cascade.cu b/src/test_cascade.cu
index 103f9dbe..ae744e27 100644
--- a/src/test_cascade.cu
+++ b/src/test_cascade.cu
@@ -136,7 +136,6 @@ void _TestVariableLengthMergeKernelCorrectness(size_t seq_len, size_t num_heads,
 template <typename T>
 void _TestMergeKernelCorrectness(size_t num_index_sets, size_t seq_len, size_t num_heads,
                                  size_t head_dim, bool sparse_s) {
-  EXPECT_GT(num_index_sets, 1) << "num_index_sets must be greater than 1";
   std::vector<T> V_host(seq_len * num_index_sets * num_heads * head_dim);
   std::vector<float> V_host_trans_f32(num_index_sets * seq_len * num_heads * head_dim);
   std::vector<float> S_host(seq_len * num_index_sets * num_heads);
@@ -178,6 +177,7 @@ void _TestMergeKernelCorrectness(size_t num_index_sets, size_t seq_len, size_t n
   thrust::device_vector<T> V_merged_1_device(seq_len * num_heads * head_dim);
   thrust::device_vector<float> S_merged_1_device(seq_len * num_heads);
 
+  if (num_index_sets > 1) {
   // Method 0: use MergeState
   MergeState(thrust::raw_pointer_cast(V_device_trans_f32.data()),
              thrust::raw_pointer_cast(S_device_trans.data()),
@@ -193,6 +193,10 @@ void _TestMergeKernelCorrectness(size_t num_index_sets, size_t seq_len, size_t n
         thrust::raw_pointer_cast(S_device_trans.data() + i * seq_len * num_heads), seq_len,
         num_heads, head_dim);
   }
+  } else {
+    V_merged_0_device = V_device;
+    S_merged_0_device = S_device;
+  }
 
   // Method 1: use MergeStates
   MergeStates(thrust::raw_pointer_cast(V_device.data()), thrust::raw_pointer_cast(S_device.data()),
@@ -478,7 +482,7 @@ void _TestTwoLevelSinglePrefixCascadeAppendCorrectness(size_t batch_size,
 
 template <typename T>
 void TestMergeKernelCorrectness() {
-  for (size_t num_index_sets : {2, 9, 81, 513}) {
+  for (size_t num_index_sets : {1, 2, 9, 81, 513}) {
     for (size_t seq_len : {4, 16, 77}) {
       for (size_t num_heads : {1, 21, 32}) {
         for (size_t head_dim : {64, 128, 256}) {