diff --git a/include/rabitqlib/core/query.hpp b/include/rabitqlib/core/query.hpp
index e053dc47..531e4846 100644
--- a/include/rabitqlib/core/query.hpp
+++ b/include/rabitqlib/core/query.hpp
@@ -30,6 +30,26 @@ class SplitSingleQuery {
 
    public:
     static constexpr size_t kNumBits = 4;
+
+    SplitSingleQuery(const SplitSingleQuery&) = default;
+    SplitSingleQuery(SplitSingleQuery&&) noexcept = default;
+    SplitSingleQuery& operator=(SplitSingleQuery&&) noexcept = default;
+
+    SplitSingleQuery& operator=(const SplitSingleQuery& other) {
+        // Copy owned codes before changing their borrowed query and corrections.
+        query_bin_ = other.query_bin_;
+        rotated_query_ = other.rotated_query_;
+        G_add_ = other.G_add_;
+        G_k1xSumq_ = other.G_k1xSumq_;
+        G_kbaseSumq_ = other.G_kbaseSumq_;
+        G_kbxSumq_ = other.G_kbxSumq_;
+        G_error_ = other.G_error_;
+        delta_ = other.delta_;
+        vl_ = other.vl_;
+        metric_type_ = other.metric_type_;
+        return *this;
+    }
+
     explicit SplitSingleQuery(
         const T* rotated_query,
         size_t padded_dim,
diff --git a/include/rabitqlib/core/rotator.hpp b/include/rabitqlib/core/rotator.hpp
index ee0f9c7c..5abaa5f2 100644
--- a/include/rabitqlib/core/rotator.hpp
+++ b/include/rabitqlib/core/rotator.hpp
@@ -214,7 +214,17 @@ class FhtKacRotator : public Rotator<float> {
 
     size_t dump_bytes() const override { return sizeof(uint8_t) * flip_.size(); }
 
-    FhtKacRotator& operator=(const FhtKacRotator&) = default;
+    FhtKacRotator(const FhtKacRotator&) = default;
+
+    FhtKacRotator& operator=(const FhtKacRotator& other) {
+        // Preserve the old dimensions if copying the sign storage fails.
+        flip_ = other.flip_;
+        this->dim_ = other.dim_;
+        this->padded_dim_ = other.padded_dim_;
+        trunc_dim_ = other.trunc_dim_;
+        fac_ = other.fac_;
+        return *this;
+    }
 
     static void kacs_walk(float* data, size_t len) { simd::kacs_walk(data, len); }
 
diff --git a/include/rabitqlib/index/detail/visited_set_hash.hpp b/include/rabitqlib/index/detail/visited_set_hash.hpp
index 9baa0f50..a79478f1 100644
--- a/include/rabitqlib/index/detail/visited_set_hash.hpp
+++ b/include/rabitqlib/index/detail/visited_set_hash.hpp
@@ -57,7 +57,13 @@ class HashBasedVisitedSet {
     ~HashBasedVisitedSet() = default;
 
     HashBasedVisitedSet(const HashBasedVisitedSet&) = default;
-    HashBasedVisitedSet& operator=(const HashBasedVisitedSet&) = default;
+    HashBasedVisitedSet& operator=(const HashBasedVisitedSet& other) {
+        if (this != &other) {
+            // Both containers may allocate; publish only a complete replacement.
+            *this = HashBasedVisitedSet(other);
+        }
+        return *this;
+    }
     HashBasedVisitedSet(HashBasedVisitedSet&&) noexcept = default;
     HashBasedVisitedSet& operator=(HashBasedVisitedSet&&) noexcept = default;