diff --git a/httplib.h b/httplib.h
index e6c5534..07310e4 100644
--- a/httplib.h
+++ b/httplib.h
@@ -577,8 +577,8 @@ using Headers =
 using Params = std::multimap<std::string, std::string>;
 using Match = std::smatch;
 
-using DownloadProgress = std::function<bool(uint64_t current, uint64_t total)>;
-using UploadProgress = std::function<bool(uint64_t current, uint64_t total)>;
+using DownloadProgress = std::function<bool(size_t current, size_t total)>;
+using UploadProgress = std::function<bool(size_t current, size_t total)>;
 
 struct Response;
 using ResponseHandler = std::function<bool(const Response &response)>;
@@ -674,9 +674,8 @@ struct FormDataProvider {
 };
 using FormDataProviderItems = std::vector<FormDataProvider>;
 
-using ContentReceiverWithProgress =
-    std::function<bool(const char *data, size_t data_length, uint64_t offset,
-                       uint64_t total_length)>;
+using ContentReceiverWithProgress = std::function<bool(
+    const char *data, size_t data_length, size_t offset, size_t total_length)>;
 
 using ContentReceiver =
     std::function<bool(const char *data, size_t data_length)>;
@@ -744,8 +743,8 @@ struct Request {
   bool has_header(const std::string &key) const;
   std::string get_header_value(const std::string &key, const char *def = "",
                                size_t id = 0) const;
-  uint64_t get_header_value_u64(const std::string &key, uint64_t def = 0,
-                                size_t id = 0) const;
+  size_t get_header_value_u64(const std::string &key, size_t def = 0,
+                              size_t id = 0) const;
   size_t get_header_value_count(const std::string &key) const;
   void set_header(const std::string &key, const std::string &val);
 
@@ -781,8 +780,8 @@ struct Response {
   bool has_header(const std::string &key) const;
   std::string get_header_value(const std::string &key, const char *def = "",
                                size_t id = 0) const;
-  uint64_t get_header_value_u64(const std::string &key, uint64_t def = 0,
-                                size_t id = 0) const;
+  size_t get_header_value_u64(const std::string &key, size_t def = 0,
+                              size_t id = 0) const;
   size_t get_header_value_count(const std::string &key) const;
   void set_header(const std::string &key, const std::string &val);
 
@@ -1334,8 +1333,8 @@ public:
   std::string get_request_header_value(const std::string &key,
                                        const char *def = "",
                                        size_t id = 0) const;
-  uint64_t get_request_header_value_u64(const std::string &key,
-                                        uint64_t def = 0, size_t id = 0) const;
+  size_t get_request_header_value_u64(const std::string &key, size_t def = 0,
+                                      size_t id = 0) const;
   size_t get_request_header_value_count(const std::string &key) const;
 
 private:
@@ -2010,9 +2009,9 @@ inline bool is_numeric(const std::string &str) {
                      [](unsigned char c) { return std::isdigit(c); });
 }
 
-inline uint64_t get_header_value_u64(const Headers &headers,
-                                     const std::string &key, uint64_t def,
-                                     size_t id, bool &is_invalid_value) {
+inline size_t get_header_value_u64(const Headers &headers,
+                                   const std::string &key, size_t def,
+                                   size_t id, bool &is_invalid_value) {
   is_invalid_value = false;
   auto rng = headers.equal_range(key);
   auto it = rng.first;
@@ -2027,22 +2026,22 @@ inline uint64_t get_header_value_u64(const Headers &headers,
   return def;
 }
 
-inline uint64_t get_header_value_u64(const Headers &headers,
-                                     const std::string &key, uint64_t def,
-                                     size_t id) {
+inline size_t get_header_value_u64(const Headers &headers,
+                                   const std::string &key, size_t def,
+                                   size_t id) {
   bool dummy = false;
   return get_header_value_u64(headers, key, def, id, dummy);
 }
 
 } // namespace detail
 
-inline uint64_t Request::get_header_value_u64(const std::string &key,
-                                              uint64_t def, size_t id) const {
+inline size_t Request::get_header_value_u64(const std::string &key, size_t def,
+                                            size_t id) const {
   return detail::get_header_value_u64(headers, key, def, id);
 }
 
-inline uint64_t Response::get_header_value_u64(const std::string &key,
-                                               uint64_t def, size_t id) const {
+inline size_t Response::get_header_value_u64(const std::string &key, size_t def,
+                                             size_t id) const {
   return detail::get_header_value_u64(headers, key, def, id);
 }
 
@@ -2228,9 +2227,9 @@ inline std::ostream &operator<<(std::ostream &os, const Error &obj) {
   return os;
 }
 
-inline uint64_t Result::get_request_header_value_u64(const std::string &key,
-                                                     uint64_t def,
-                                                     size_t id) const {
+inline size_t Result::get_request_header_value_u64(const std::string &key,
+                                                   size_t def,
+                                                   size_t id) const {
   return detail::get_header_value_u64(request_headers_, key, def, id);
 }
 
@@ -4617,19 +4616,19 @@ inline bool read_headers(Stream &strm, Headers &headers) {
   return true;
 }
 
-inline bool read_content_with_length(Stream &strm, uint64_t len,
+inline bool read_content_with_length(Stream &strm, size_t len,
                                      DownloadProgress progress,
                                      ContentReceiverWithProgress out) {
   char buf[CPPHTTPLIB_RECV_BUFSIZ];
 
-  uint64_t r = 0;
+  size_t r = 0;
   while (r < len) {
     auto read_len = static_cast<size_t>(len - r);
     auto n = strm.read(buf, (std::min)(read_len, CPPHTTPLIB_RECV_BUFSIZ));
     if (n <= 0) { return false; }
 
     if (!out(buf, static_cast<size_t>(n), r, len)) { return false; }
-    r += static_cast<uint64_t>(n);
+    r += static_cast<size_t>(n);
 
     if (progress) {
       if (!progress(r, len)) { return false; }
@@ -4639,14 +4638,14 @@ inline bool read_content_with_length(Stream &strm, uint64_t len,
   return true;
 }
 
-inline void skip_content_with_length(Stream &strm, uint64_t len) {
+inline void skip_content_with_length(Stream &strm, size_t len) {
   char buf[CPPHTTPLIB_RECV_BUFSIZ];
-  uint64_t r = 0;
+  size_t r = 0;
   while (r < len) {
     auto read_len = static_cast<size_t>(len - r);
     auto n = strm.read(buf, (std::min)(read_len, CPPHTTPLIB_RECV_BUFSIZ));
     if (n <= 0) { return; }
-    r += static_cast<uint64_t>(n);
+    r += static_cast<size_t>(n);
   }
 }
 
@@ -4660,7 +4659,7 @@ inline ReadContentResult
 read_content_without_length(Stream &strm, size_t payload_max_length,
                             ContentReceiverWithProgress out) {
   char buf[CPPHTTPLIB_RECV_BUFSIZ];
-  uint64_t r = 0;
+  size_t r = 0;
   for (;;) {
     auto n = strm.read(buf, CPPHTTPLIB_RECV_BUFSIZ);
     if (n == 0) { return ReadContentResult::Success; }
@@ -4668,14 +4667,14 @@ read_content_without_length(Stream &strm, size_t payload_max_length,
 
     // Check if adding this data would exceed the payload limit
     if (r > payload_max_length ||
-        payload_max_length - r < static_cast<uint64_t>(n)) {
+        payload_max_length - r < static_cast<size_t>(n)) {
       return ReadContentResult::PayloadTooLarge;
     }
 
     if (!out(buf, static_cast<size_t>(n), r, 0)) {
       return ReadContentResult::Error;
     }
-    r += static_cast<uint64_t>(n);
+    r += static_cast<size_t>(n);
   }
 
   return ReadContentResult::Success;
@@ -4693,7 +4692,7 @@ inline ReadContentResult read_content_chunked(Stream &strm, T &x,
   if (!line_reader.getline()) { return ReadContentResult::Error; }
 
   unsigned long chunk_len;
-  uint64_t total_len = 0;
+  size_t total_len = 0;
   while (true) {
     char *end_ptr;
 
@@ -4845,7 +4844,7 @@ bool prepare_content_receiver(T &x, int &status,
     if (decompressor) {
       if (decompressor->is_valid()) {
         ContentReceiverWithProgress out = [&](const char *buf, size_t n,
-                                              uint64_t off, uint64_t len) {
+                                              size_t off, size_t len) {
           return decompressor->decompress(buf, n,
                                           [&](const char *buf2, size_t n2) {
                                             return receiver(buf2, n2, off, len);
@@ -4859,8 +4858,8 @@ bool prepare_content_receiver(T &x, int &status,
     }
   }
 
-  ContentReceiverWithProgress out = [&](const char *buf, size_t n, uint64_t off,
-                                        uint64_t len) {
+  ContentReceiverWithProgress out = [&](const char *buf, size_t n, size_t off,
+                                        size_t len) {
     return receiver(buf, n, off, len);
   };
   return callback(std::move(out));
@@ -4899,9 +4898,9 @@ bool read_content(Stream &strm, T &x, size_t payload_max_length, int &status,
           }
         } else {
           auto is_invalid_value = false;
-          auto len = get_header_value_u64(
-              x.headers, "Content-Length",
-              (std::numeric_limits<uint64_t>::max)(), 0, is_invalid_value);
+          auto len = get_header_value_u64(x.headers, "Content-Length",
+                                          (std::numeric_limits<size_t>::max)(),
+                                          0, is_invalid_value);
 
           if (is_invalid_value) {
             ret = false;
@@ -7568,13 +7567,13 @@ inline bool Server::read_content_core(
     }
 
     multipart_form_data_parser.set_boundary(std::move(boundary));
-    out = [&](const char *buf, size_t n, uint64_t /*off*/, uint64_t /*len*/) {
+    out = [&](const char *buf, size_t n, size_t /*off*/, size_t /*len*/) {
       return multipart_form_data_parser.parse(buf, n, multipart_header,
                                               multipart_receiver);
     };
   } else {
-    out = [receiver](const char *buf, size_t n, uint64_t /*off*/,
-                     uint64_t /*len*/) { return receiver(buf, n); };
+    out = [receiver](const char *buf, size_t n, size_t /*off*/,
+                     size_t /*len*/) { return receiver(buf, n); };
   }
 
   if (req.method == "DELETE" && !req.has_header("Content-Length")) {
@@ -9093,21 +9092,21 @@ inline bool ClientImpl::process_request(Stream &strm, Request &req,
     auto out =
         req.content_receiver
             ? static_cast<ContentReceiverWithProgress>(
-                  [&](const char *buf, size_t n, uint64_t off, uint64_t len) {
+                  [&](const char *buf, size_t n, size_t off, size_t len) {
                     if (redirect) { return true; }
                     auto ret = req.content_receiver(buf, n, off, len);
                     if (!ret) { error = Error::Canceled; }
                     return ret;
                   })
             : static_cast<ContentReceiverWithProgress>(
-                  [&](const char *buf, size_t n, uint64_t /*off*/,
-                      uint64_t /*len*/) {
+                  [&](const char *buf, size_t n, size_t /*off*/,
+                      size_t /*len*/) {
                     assert(res.body.size() + n <= res.body.max_size());
                     res.body.append(buf, n);
                     return true;
                   });
 
-    auto progress = [&](uint64_t current, uint64_t total) {
+    auto progress = [&](size_t current, size_t total) {
       if (!req.download_progress || redirect) { return true; }
       auto ret = req.download_progress(current, total);
       if (!ret) { error = Error::Canceled; }
@@ -9258,7 +9257,7 @@ inline Result ClientImpl::Get(const std::string &path, const Headers &headers,
   req.response_handler = std::move(response_handler);
   req.content_receiver =
       [content_receiver](const char *data, size_t data_length,
-                         uint64_t /*offset*/, uint64_t /*total_length*/) {
+                         size_t /*offset*/, size_t /*total_length*/) {
         return content_receiver(data, data_length);
       };
   req.download_progress = std::move(progress);
@@ -9448,7 +9447,7 @@ inline Result ClientImpl::Post(const std::string &path, const Headers &headers,
   req.body = body;
   req.content_receiver =
       [content_receiver](const char *data, size_t data_length,
-                         uint64_t /*offset*/, uint64_t /*total_length*/) {
+                         size_t /*offset*/, size_t /*total_length*/) {
         return content_receiver(data, data_length);
       };
   req.download_progress = std::move(progress);
@@ -9600,7 +9599,7 @@ inline Result ClientImpl::Put(const std::string &path, const Headers &headers,
   req.body = body;
   req.content_receiver =
       [content_receiver](const char *data, size_t data_length,
-                         uint64_t /*offset*/, uint64_t /*total_length*/) {
+                         size_t /*offset*/, size_t /*total_length*/) {
         return content_receiver(data, data_length);
       };
   req.download_progress = std::move(progress);
@@ -9755,7 +9754,7 @@ inline Result ClientImpl::Patch(const std::string &path, const Headers &headers,
   req.body = body;
   req.content_receiver =
       [content_receiver](const char *data, size_t data_length,
-                         uint64_t /*offset*/, uint64_t /*total_length*/) {
+                         size_t /*offset*/, size_t /*total_length*/) {
         return content_receiver(data, data_length);
       };
   req.download_progress = std::move(progress);