diff --git a/cpp/src/groupby/hash/global_memory_aggregator.cuh b/cpp/src/groupby/hash/global_memory_aggregator.cuh
index 9b646313239..86769df9b4b 100644
--- a/cpp/src/groupby/hash/global_memory_aggregator.cuh
+++ b/cpp/src/groupby/hash/global_memory_aggregator.cuh
@@ -266,6 +266,8 @@ struct gmem_element_aggregator {
                              bool* source_mask,
                              cudf::size_type source_index) const noexcept
   {
+    // Early exit for all aggregation kinds since shared memory aggregation of
+    // `COUNT_ALL` is always valid
     if (!source_mask[source_index]) { return; }
 
     update_target_element_gmem<Source, k>{}(
diff --git a/cpp/src/groupby/hash/shared_memory_aggregator.cuh b/cpp/src/groupby/hash/shared_memory_aggregator.cuh
index 49524c25545..94fe77a87ab 100644
--- a/cpp/src/groupby/hash/shared_memory_aggregator.cuh
+++ b/cpp/src/groupby/hash/shared_memory_aggregator.cuh
@@ -255,6 +255,7 @@ struct shmem_element_aggregator {
                              cudf::column_device_view source,
                              cudf::size_type source_index) const noexcept
   {
+    // Check nullability for all aggregation kinds but `COUNT_ALL`
     if constexpr (k != cudf::aggregation::COUNT_ALL) {
       if (source.is_null(source_index)) { return; }
     }