diff --git a/include/rabitqlib/core/detail/rabitq_impl.hpp b/include/rabitqlib/core/detail/rabitq_impl.hpp
index 79ca6c8e..1992291d 100644
--- a/include/rabitqlib/core/detail/rabitq_impl.hpp
+++ b/include/rabitqlib/core/detail/rabitq_impl.hpp
@@ -820,9 +820,9 @@ static inline void rabitq_scalar_impl(
     RowMajorArrayMap<TP> total_code_arr(total_code, 1, dim);
     RowMajorArray<T> u_cb = total_code_arr.template cast<T>() + cb;
 
-    float norm_data = std::sqrt(l2norm_sqr(residual_arr.data(), dim));
-    float norm_quan = std::sqrt(l2norm_sqr(u_cb.data(), dim));
-    float cos_similarity =
+    T norm_data = std::sqrt(l2norm_sqr(residual_arr.data(), dim));
+    T norm_quan = std::sqrt(l2norm_sqr(u_cb.data(), dim));
+    T cos_similarity =
         dot_product<T>(residual_arr.data(), u_cb.data(), dim) / (norm_data * norm_quan);
 
     if (scalar_quantizer_type == ScalarQuantizerType::RECONSTRUCTION) {
diff --git a/include/rabitqlib/fastscan/detail/lut.hpp b/include/rabitqlib/fastscan/detail/lut.hpp
index 1b74d77e..8a876908 100644
--- a/include/rabitqlib/fastscan/detail/lut.hpp
+++ b/include/rabitqlib/fastscan/detail/lut.hpp
@@ -129,6 +129,19 @@ class Lut {
     explicit Lut(const T* rotated_query, size_t padded_dim, bool use_hacc = false)
         : Lut(rotated_query, padded_dim, use_hacc, checked_shape(padded_dim, use_hacc)) {}
 
+    Lut(const Lut&) = default;
+    Lut(Lut&&) noexcept = default;
+    Lut& operator=(Lut&&) noexcept = default;
+
+    Lut& operator=(const Lut& other) {
+        // Copy bytes before metadata: allocation failure must preserve the old shape.
+        lut_ = other.lut_;
+        table_length_ = other.table_length_;
+        delta_ = other.delta_;
+        sum_vl_lut_ = other.sum_vl_lut_;
+        return *this;
+    }
+
     /**
      * Reinitialize owned LUT bytes while reusing their allocation. Scratch buffers
      * are borrowed only for this call and may be overwritten/released afterwards.
diff --git a/include/rabitqlib/fastscan/query.hpp b/include/rabitqlib/fastscan/query.hpp
index bfe1f1d1..65d21c35 100644
--- a/include/rabitqlib/fastscan/query.hpp
+++ b/include/rabitqlib/fastscan/query.hpp
@@ -131,6 +131,22 @@ class SplitBatchQuery {
    public:
     explicit SplitBatchQuery() = default;
 
+    SplitBatchQuery(const SplitBatchQuery&) = default;
+    SplitBatchQuery(SplitBatchQuery&&) noexcept = default;
+    SplitBatchQuery& operator=(SplitBatchQuery&&) noexcept = default;
+
+    SplitBatchQuery& operator=(const SplitBatchQuery& other) {
+        // Keep the borrowed query and corrections paired with the LUT if copying fails.
+        lookup_table_ = other.lookup_table_;
+        rotated_query_ = other.rotated_query_;
+        G_add_ = other.G_add_;
+        G_error_ = other.G_error_;
+        G_k1xSumq_ = other.G_k1xSumq_;
+        G_kbxSumq_ = other.G_kbxSumq_;
+        metric_type_ = other.metric_type_;
+        return *this;
+    }
+
     explicit SplitBatchQuery(
         const T* rotated_query,
         size_t padded_dim,
diff --git a/include/rabitqlib/index/detail/visited_set_hash.hpp b/include/rabitqlib/index/detail/visited_set_hash.hpp
index 6c19fafc..9baa0f50 100644
--- a/include/rabitqlib/index/detail/visited_set_hash.hpp
+++ b/include/rabitqlib/index/detail/visited_set_hash.hpp
@@ -42,11 +42,12 @@ class HashBasedVisitedSet {
     [[nodiscard]] auto hash1(const PID value) const { return value & mask_; }
 
     void initialize_table(const size_t table_size) {
+        // Allocate before changing the mask so failure preserves the previous table.
+        table_ = std::vector<PID, memory::AlignedAllocator<PID>>(table_size);
         table_size_ = table_size;
         mask_ = static_cast<PID>(table_size_ - 1);
         assert(hash1(static_cast<PID>(table_size)) == 0);
 
-        table_ = std::vector<PID, memory::AlignedAllocator<PID>>(table_size);
         std::fill(table_.begin(), table_.end(), kPidMax);
         stl_hash_.clear();
     }
diff --git a/python_bindings/ivf_bindings.cpp b/python_bindings/ivf_bindings.cpp
index 68304632..20b81065 100644
--- a/python_bindings/ivf_bindings.cpp
+++ b/python_bindings/ivf_bindings.cpp
@@ -119,11 +119,16 @@ class IvfIndex {
         const auto* data_ptr = data_array.data();
         const auto* centroids_ptr = centroids_array.data();
         const auto* cluster_ids_ptr = cluster_ids_vec.data();
-        {
+        try {
             py::gil_scoped_release release;
             index_->construct(
                 data_ptr, centroids_ptr, cluster_ids_ptr, fast_quantization, num_threads
             );
+        } catch (...) {
+            // Early failures preserve the old index; allocation can invalidate it.
+            // Stored count remains nonzero even when every point was removed.
+            built_ = index_->num_stored_points() != 0;
+            throw;
         }
         built_ = true;
     }