diff --git a/include/pq_flash_index.h b/include/pq_flash_index.h
index befde1a1a..cf504efdd 100644
--- a/include/pq_flash_index.h
+++ b/include/pq_flash_index.h
@@ -254,6 +254,12 @@ template <typename T, typename LabelT = uint32_t> class PQFlashIndex
     tsl::robin_map<uint32_t, std::vector<uint32_t>> _real_to_dummy_map;
     std::unordered_map<std::string, LabelT> _label_map;
 
+    // Validate if data type is correct by check each data's vector/neighbor section.
+    // disk_nnodes, total node count in index, used to validate neighbor index of each node.
+    // contains_disk_pq_file, flag if indices contains disk pq file(suffix : _disk.index_pq_pivots.bin);
+    // If it's true, max_node_len use uint8 to calculate data size instead.(check aux_utils.cpp:1399)
+    bool validate_vector_data_type(uint64_t disk_nnodes, bool contains_disk_pq_file);
+
 #ifdef EXEC_ENV_OLS
     // Set to a larger value than the actual header to accommodate
     // any additions we make to the header. This is an outer limit
diff --git a/src/pq_flash_index.cpp b/src/pq_flash_index.cpp
index 179e9a71e..88f71de5c 100644
--- a/src/pq_flash_index.cpp
+++ b/src/pq_flash_index.cpp
@@ -1209,7 +1209,13 @@ int PQFlashIndex<T, LabelT>::load_from_separate_paths(uint32_t num_threads, cons
     this->_max_nthreads = num_threads;
 
 #endif
-
+    // Validate data type (called once for both EXEC_ENV_OLS and non-OLS paths)
+    if (!validate_vector_data_type(disk_nnodes, _use_disk_index_pq))
+    {
+        throw diskann::ANNException("Data type validation failed. Please ensure --data_type matches "
+                                    "the type used when building the index.",
+                                    -1, __FUNCSIG__, __FILE__, __LINE__);
+    }
 #ifdef EXEC_ENV_OLS
     if (files.fileExists(medoids_file))
     {
@@ -1768,7 +1774,7 @@ void PQFlashIndex<T, LabelT>::cached_beam_search(const T *query1, const uint64_t
             {
                 full_retset.push_back(Neighbor(frontier_nhood.first, cur_expanded_dist));
             }
-            
+
             uint32_t *node_nbrs = (node_buf + 1);
             // compute node_nbrs <-> query dist in PQ space
             cpu_timer.reset();
@@ -1971,6 +1977,91 @@ template <typename T, typename LabelT> char *PQFlashIndex<T, LabelT>::getHeaderB
 }
 #endif
 
+template <typename T, typename LabelT>
+bool PQFlashIndex<T, LabelT>::validate_vector_data_type(uint64_t disk_nnodes, bool contains_disk_pq_file)
+{
+    (void)contains_disk_pq_file; // Suppress unused parameter warning
+
+    // Use _disk_bytes_per_point which is already set correctly:
+    // - For disk PQ: _disk_pq_n_chunks * sizeof(uint8_t)
+    // - For regular: _data_dim * sizeof(T)
+    size_t vector_length = _disk_bytes_per_point;
+    if (vector_length + sizeof(uint32_t) >= _max_node_len)
+    {
+        diskann::cerr << "Vector length : " << vector_length << " and neighbor count size : " << sizeof(uint32_t)
+                      << ", expected less than max node length : " << _max_node_len << std::endl;
+        diskann::cerr << "Please check if wrong data type with larger size is "
+                         "specified, like use float type to load byte index!"
+                      << std::endl;
+        return false;
+    }
+
+    // Borrow thread data for the read
+    ScratchStoreManager<SSDThreadData<T>> manager(this->_thread_data);
+    auto this_thread_data = manager.scratch_space();
+    IOContext &ctx = this_thread_data->ctx;
+
+    // Calculate the number of sectors needed per node
+    uint64_t num_sectors_per_node = _nnodes_per_sector > 0 ? 1 : DIV_ROUND_UP(_max_node_len, defaults::SECTOR_LEN);
+
+    // Allocate sector-aligned buffer (required for direct I/O)
+    char *buf = nullptr;
+    alloc_aligned((void **)&buf, num_sectors_per_node * defaults::SECTOR_LEN, defaults::SECTOR_LEN);
+
+    // Read sector(s) containing node 0
+    uint64_t node_sector = get_node_sector(0);
+    AlignedRead read_request(node_sector * defaults::SECTOR_LEN, num_sectors_per_node * defaults::SECTOR_LEN, buf);
+    std::vector<AlignedRead> read_requests;
+    read_requests.emplace_back(read_request);
+    reader->read(read_requests, ctx);
+
+#if defined(_WINDOWS) && defined(USE_BING_INFRA)
+    if ((*ctx.m_pRequestsStatus)[0] != IOContext::READ_SUCCESS)
+    {
+        aligned_free(buf);
+        diskann::cerr << "Read disk index file " << _disk_index_file << " failed, can't validate data type!"
+                      << std::endl;
+        return false;
+    }
+#endif
+
+    // Use offset_to_node to get correct position within the sector buffer for node 0
+    char *first_node = offset_to_node(buf, 0);
+    
+    // Use offset_to_node_nhood which correctly uses _disk_bytes_per_point
+    uint32_t *neighbors = offset_to_node_nhood(first_node);
+    uint32_t neighbor_count = *neighbors;
+
+    // Calculate max degree based on the assumed vector length
+    // max_node_len = vector_length + sizeof(uint32_t) + max_degree * sizeof(uint32_t)
+    // So: max_degree = (max_node_len - vector_length - sizeof(uint32_t)) / sizeof(uint32_t)
+    uint32_t max_degree = static_cast<uint32_t>((_max_node_len - vector_length - sizeof(uint32_t)) / sizeof(uint32_t));
+
+    if (neighbor_count > max_degree)
+    {
+        aligned_free(buf);
+        diskann::cerr << "Calculated max neighbor count : " << max_degree
+                      << " and first node neighbor count : " << neighbor_count << ", load data type is not correct!"
+                      << std::endl;
+        return false;
+    }
+
+    for (uint32_t i = 1; i <= neighbor_count; ++i)
+    {
+        if (neighbors[i] >= disk_nnodes)
+        {
+            aligned_free(buf);
+            diskann::cerr << "Neighbor[" << i - 1 << "], index : " << neighbors[i]
+                          << ", greater than total node count : " << disk_nnodes << ", load data type is not correct!"
+                          << std::endl;
+            return false;
+        }
+    }
+
+    aligned_free(buf);
+    return true;
+}
+
 template <typename T, typename LabelT>
 std::vector<std::uint8_t> PQFlashIndex<T, LabelT>::get_pq_vector(std::uint64_t vid)
 {