diff --git a/include/miniocpp/args.h b/include/miniocpp/args.h
index 1987092..ded4a4f 100644
--- a/include/miniocpp/args.h
+++ b/include/miniocpp/args.h
@@ -382,7 +382,7 @@ struct ComposeSource : public ObjectConditionalReadArgs {
   utils::Multimap Headers() const;
 
  private:
-  long object_size_ = -1;
+  std::optional<size_t> object_size_;
   utils::Multimap headers_;
 };  // struct ComposeSource
 
diff --git a/include/miniocpp/types.h b/include/miniocpp/types.h
index 5be1ae4..98e2910 100644
--- a/include/miniocpp/types.h
+++ b/include/miniocpp/types.h
@@ -25,6 +25,7 @@
 #include <map>
 #include <memory>
 #include <nlohmann/json_fwd.hpp>
+#include <optional>
 #include <ostream>
 #include <string>
 #include <type_traits>
@@ -293,17 +294,18 @@ struct SelectRequest {
 struct SelectResult {
   error::Error err = error::SUCCESS;
   bool ended = false;
-  long int bytes_scanned = -1;
-  long int bytes_processed = -1;
-  long int bytes_returned = -1;
+  std::optional<long long> bytes_scanned;
+  std::optional<long long> bytes_processed;
+  std::optional<long long> bytes_returned;
   std::string records;
 
   SelectResult() : ended(true) {}
 
   explicit SelectResult(error::Error err) : err(std::move(err)), ended(true) {}
 
-  SelectResult(long int bytes_scanned, long int bytes_processed,
-               long int bytes_returned)
+  SelectResult(std::optional<long long> bytes_scanned,
+               std::optional<long long> bytes_processed,
+               std::optional<long long> bytes_returned)
       : bytes_scanned(bytes_scanned),
         bytes_processed(bytes_processed),
         bytes_returned(bytes_returned) {}
diff --git a/src/args.cc b/src/args.cc
index deb8e02..e4a89eb 100644
--- a/src/args.cc
+++ b/src/args.cc
@@ -381,7 +381,7 @@ error::Error ComposeSource::BuildHeaders(size_t object_size,
     }
   }
 
-  object_size_ = static_cast<long>(object_size);
+  object_size_ = object_size;
   headers_ = CopyHeaders();
   if (!headers_.Contains("x-amz-copy-source-if-match")) {
     headers_.Add("x-amz-copy-source-if-match", etag);
@@ -391,14 +391,14 @@ error::Error ComposeSource::BuildHeaders(size_t object_size,
 }
 
 size_t ComposeSource::ObjectSize() const {
-  if (object_size_ == -1) {
+  if (!object_size_.has_value()) {
     std::cerr << "ABORT: ComposeSource::BuildHeaders() must be called prior to "
                  "this method invocation. This should not happen."
               << std::endl;
     std::terminate();
   }
 
-  return object_size_;
+  return *object_size_;
 }
 
 utils::Multimap ComposeSource::Headers() const {
diff --git a/src/baseclient.cc b/src/baseclient.cc
index 492f501..1196cf4 100644
--- a/src/baseclient.cc
+++ b/src/baseclient.cc
@@ -2049,7 +2049,7 @@ Result<StatObjectResponse> BaseClient::StatObject(StatObjectArgs args) {
   resp.etag = utils::Trim(response->headers.GetFront("etag"), '"');
 
   std::string value = response->headers.GetFront("content-length");
-  if (!value.empty()) resp.size = std::stol(value);
+  if (!value.empty()) resp.size = std::stoll(value);
 
   value = response->headers.GetFront("last-modified");
   if (!value.empty()) {
diff --git a/src/client.cc b/src/client.cc
index c1045d7..433305e 100644
--- a/src/client.cc
+++ b/src/client.cc
@@ -1165,7 +1165,8 @@ Result<DownloadObjectResponse> Client::DownloadObject(DownloadObjectArgs args) {
 
   std::string temp_filename =
       args.filename + "." + curlpp::escape(etag) + ".part.minio";
-  std::ofstream fout(temp_filename, std::ios::trunc | std::ios::out);
+  std::ofstream fout(temp_filename,
+                     std::ios::trunc | std::ios::out | std::ios::binary);
   if (!fout.is_open()) {
     return error::make<DownloadObjectResponse>("unable to open file " +
                                                temp_filename);
diff --git a/src/select.cc b/src/select.cc
index ce6c4db..6851b35 100644
--- a/src/select.cc
+++ b/src/select.cc
@@ -195,21 +195,21 @@ bool SelectHandler::process(const http::DataFunctionArgs& /* args */,
     auto root = xdoc.select_node(xpath.c_str());
     pugi::xpath_node text;
     std::string value;
-    long int bytes_scanned = -1;
-    long int bytes_processed = -1;
-    long int bytes_returned = -1;
+    std::optional<long long> bytes_scanned;
+    std::optional<long long> bytes_processed;
+    std::optional<long long> bytes_returned;
 
     text = root.node().select_node("BytesScanned/text()");
     value = text.node().value();
-    if (!value.empty()) bytes_scanned = std::stol(value);
+    if (!value.empty()) bytes_scanned = std::stoll(value);
 
     text = root.node().select_node("BytesProcessed/text()");
     value = text.node().value();
-    if (!value.empty()) bytes_processed = std::stol(value);
+    if (!value.empty()) bytes_processed = std::stoll(value);
 
     text = root.node().select_node("BytesReturned/text()");
     value = text.node().value();
-    if (!value.empty()) bytes_returned = std::stol(value);
+    if (!value.empty()) bytes_returned = std::stoll(value);
 
     cont = result_func_(
         SelectResult(bytes_scanned, bytes_processed, bytes_returned));
diff --git a/tests/tests.cc b/tests/tests.cc
index 7d4de3b..ae85426 100644
--- a/tests/tests.cc
+++ b/tests/tests.cc
@@ -22,6 +22,7 @@
 #include <miniocpp/request.h>
 #include <miniocpp/response.h>
 #include <miniocpp/result.h>
+#include <miniocpp/select.h>
 #include <miniocpp/types.h>
 
 using minio::Result;
@@ -38,6 +39,7 @@ using minio::Result;
 #include <iosfwd>
 #include <iostream>
 #include <list>
+#include <map>
 #include <ostream>
 #include <random>
 #include <sstream>
@@ -102,6 +104,43 @@ std::string RandBucketName() {
 
 std::string RandObjectName() { return RandomString(charset, 8); }
 
+std::string PutUint32BigEndian(unsigned int v) {
+  std::string s(4, '\0');
+  s[0] = static_cast<char>((v >> 24) & 0xFF);
+  s[1] = static_cast<char>((v >> 16) & 0xFF);
+  s[2] = static_cast<char>((v >> 8) & 0xFF);
+  s[3] = static_cast<char>(v & 0xFF);
+  return s;
+}
+
+// Build a single S3 Select protocol frame (prelude + prelude CRC + headers
+// + payload + message CRC) for the given event headers and XML payload.
+std::string MakeSelectFrame(const std::map<std::string, std::string>& headers,
+                            const std::string& payload) {
+  std::string headerdata;
+  for (const auto& [name, value] : headers) {
+    headerdata += static_cast<char>(name.length());
+    headerdata += name;
+    headerdata += static_cast<char>(7);  // header value type: string
+    headerdata += static_cast<char>((value.length() >> 8) & 0xFF);
+    headerdata += static_cast<char>(value.length() & 0xFF);
+    headerdata += value;
+  }
+  headerdata += static_cast<char>(0);  // header terminator
+
+  std::string data = headerdata + payload;
+  unsigned int total_length = 16 + static_cast<unsigned int>(data.length());
+  std::string prelude =
+      PutUint32BigEndian(total_length) +
+      PutUint32BigEndian(static_cast<unsigned int>(headerdata.length()));
+  std::string prelude_crc = PutUint32BigEndian(
+      static_cast<unsigned int>(minio::utils::CRC32(prelude)));
+  std::string message = prelude + prelude_crc + data;
+  std::string message_crc = PutUint32BigEndian(
+      static_cast<unsigned int>(minio::utils::CRC32(message)));
+  return message + message_crc;
+}
+
 struct MakeBucketError : public std::runtime_error {
   MakeBucketError(std::string err) : runtime_error(err) {}
 };
@@ -1537,6 +1576,58 @@ class Tests {
       RemoveObject(bucket_name_, object_name);
     }
   }  // TestAsyncOperations
+
+  // Regression test for SelectHandler Stats metric parsing: metrics larger
+  // than INT32_MAX must round-trip as exact long long values (any fallback
+  // to std::stol on 32-bit Windows LLP64 would truncate them). Uses a
+  // synthetic Stats event frame, independent of large objects.
+  void SelectStatsMetrics() {
+    std::cout << "SelectStatsMetrics()" << std::endl;
+
+    const long long scanned = 5000000000LL;
+    const long long processed = 6000000000LL;
+    const long long returned = 7000000000LL;
+
+    std::map<std::string, std::string> headers = {
+        {":message-type", "event"},
+        {":event-type", "Stats"},
+    };
+    std::string payload = "<Stats><BytesScanned>" + std::to_string(scanned) +
+                          "</BytesScanned><BytesProcessed>" +
+                          std::to_string(processed) +
+                          "</BytesProcessed><BytesReturned>" +
+                          std::to_string(returned) + "</BytesReturned></Stats>";
+
+    bool stats_delivered = false;
+    minio::s3::SelectHandler handler(
+        [&](minio::s3::SelectResult result) -> bool {
+          if (result.err) {
+            throw std::runtime_error("SelectStatsMetrics(): " +
+                                     result.err.String());
+          }
+          if (!result.bytes_scanned.has_value() ||
+              *result.bytes_scanned != scanned ||
+              !result.bytes_processed.has_value() ||
+              *result.bytes_processed != processed ||
+              !result.bytes_returned.has_value() ||
+              *result.bytes_returned != returned) {
+            throw std::runtime_error(
+                "SelectStatsMetrics(): unexpected metrics");
+          }
+          stats_delivered = true;
+          return true;
+        });
+
+    minio::http::DataFunctionArgs args;
+    args.datachunk = MakeSelectFrame(headers, payload);
+    if (!handler.DataFunction(args)) {
+      throw std::runtime_error("SelectStatsMetrics(): DataFunction failed");
+    }
+    if (!stats_delivered) {
+      throw std::runtime_error(
+          "SelectStatsMetrics(): Stats result was not delivered");
+    }
+  }
 };  // class Tests
 
 int main(int /*argc*/, char* /*argv*/[]) {
@@ -1596,6 +1687,7 @@ int main(int /*argc*/, char* /*argv*/[]) {
   tests.SelectObjectContent();
   tests.ListenBucketNotification();
   tests.TestAsyncOperations();
+  tests.SelectStatsMetrics();
 
   return EXIT_SUCCESS;
 }