diff --git a/cpp/include/raft/neighbors/brute_force-inl.cuh b/cpp/include/raft/neighbors/brute_force-inl.cuh
index b4de76037a..bc9e09e5b0 100644
--- a/cpp/include/raft/neighbors/brute_force-inl.cuh
+++ b/cpp/include/raft/neighbors/brute_force-inl.cuh
@@ -90,10 +90,14 @@ inline void knn_merge_parts(
   RAFT_EXPECTS(in_keys.extent(1) == in_values.extent(1) && in_keys.extent(0) == in_values.extent(0),
                "in_keys and in_values must have the same shape.");
   RAFT_EXPECTS(
-    out_keys.extent(0) == out_values.extent(0) == n_samples,
+    out_keys.extent(0) == out_values.extent(0) && out_keys.extent(0) == n_samples,
     "Number of rows in output keys and val matrices must equal number of rows in search matrix.");
-  RAFT_EXPECTS(out_keys.extent(1) == out_values.extent(1) == in_keys.extent(1),
-               "Number of columns in output indices and distances matrices must be equal to k");
+  RAFT_EXPECTS(
+    out_keys.extent(1) == out_values.extent(1) && out_keys.extent(1) == in_keys.extent(1),
+    "Number of columns in output indices and distances matrices must be equal to k");
+
+  idx_t* translations_ptr = nullptr;
+  if (translations.has_value()) { translations_ptr = translations.value().data_handle(); }
 
   auto n_parts = in_keys.extent(0) / n_samples;
   detail::knn_merge_parts(in_keys.data_handle(),
@@ -104,7 +108,7 @@ inline void knn_merge_parts(
                           n_parts,
                           in_keys.extent(1),
                           resource::get_cuda_stream(handle),
-                          translations.value_or(nullptr));
+                          translations_ptr);
 }
 
 /**
diff --git a/cpp/include/raft/neighbors/detail/knn_merge_parts.cuh b/cpp/include/raft/neighbors/detail/knn_merge_parts.cuh
index e2b5c41fb0..0a33832b79 100644
--- a/cpp/include/raft/neighbors/detail/knn_merge_parts.cuh
+++ b/cpp/include/raft/neighbors/detail/knn_merge_parts.cuh
@@ -30,8 +30,8 @@ template <typename value_idx = std::int64_t,
           int warp_q,
           int thread_q,
           int tpb>
-__global__ void knn_merge_parts_kernel(value_t* inK,
-                                       value_idx* inV,
+__global__ void knn_merge_parts_kernel(const value_t* inK,
+                                       const value_idx* inV,
                                        value_t* outK,
                                        value_idx* outV,
                                        size_t n_samples,
@@ -65,8 +65,8 @@ __global__ void knn_merge_parts_kernel(value_t* inK,
 
   int col = i % k;
 
-  value_t* inKStart   = inK + (row_idx + col);
-  value_idx* inVStart = inV + (row_idx + col);
+  const value_t* inKStart   = inK + (row_idx + col);
+  const value_idx* inVStart = inV + (row_idx + col);
 
   int limit             = Pow2<WarpSize>::roundDown(total_k);
   value_idx translation = 0;
@@ -99,8 +99,8 @@ __global__ void knn_merge_parts_kernel(value_t* inK,
 }
 
 template <typename value_idx = std::int64_t, typename value_t = float, int warp_q, int thread_q>
-inline void knn_merge_parts_impl(value_t* inK,
-                                 value_idx* inV,
+inline void knn_merge_parts_impl(const value_t* inK,
+                                 const value_idx* inV,
                                  value_t* outK,
                                  value_idx* outV,
                                  size_t n_samples,
@@ -137,8 +137,8 @@ inline void knn_merge_parts_impl(value_t* inK,
  * @param translations mapping of index offsets for each partition
  */
 template <typename value_idx = std::int64_t, typename value_t = float>
-inline void knn_merge_parts(value_t* inK,
-                            value_idx* inV,
+inline void knn_merge_parts(const value_t* inK,
+                            const value_idx* inV,
                             value_t* outK,
                             value_idx* outV,
                             size_t n_samples,
diff --git a/cpp/include/raft/spatial/knn/knn.cuh b/cpp/include/raft/spatial/knn/knn.cuh
index 7b088316a3..3c089b1d22 100644
--- a/cpp/include/raft/spatial/knn/knn.cuh
+++ b/cpp/include/raft/spatial/knn/knn.cuh
@@ -50,8 +50,8 @@ namespace raft::spatial::knn {
  * @param translations
  */
 template <typename idx_t = int64_t, typename value_t = float>
-inline void knn_merge_parts(value_t* in_keys,
-                            idx_t* in_values,
+inline void knn_merge_parts(const value_t* in_keys,
+                            const idx_t* in_values,
                             value_t* out_keys,
                             idx_t* out_values,
                             size_t n_samples,