diff --git a/twml/libtwml/include/twml/BlockFormatWriter.h b/twml/libtwml/include/twml/BlockFormatWriter.h
index 2b7eb710a..c3821abd1 100644
--- a/twml/libtwml/include/twml/BlockFormatWriter.h
+++ b/twml/libtwml/include/twml/BlockFormatWriter.h
@@ -33,7 +33,7 @@ namespace twml {
         int record_index_;
         int records_per_block_;
 
-        int pack_tag_and_wiretype(std::fstream& fs, uint32_t tag, uint32_t wiretype);
+        int pack_tag_and_wiretype(std::fstream& fs, std::uint32_t tag, std::uint32_t wiretype);
         int pack_varint_i32(std::fstream& fs, int value);
         int pack_string(std::fstream& fs, const char *in, size_t in_len);
         int write_int(std::fstream& fs, int value);
diff --git a/twml/libtwml/src/lib/BlockFormatWriter.cpp b/twml/libtwml/src/lib/BlockFormatWriter.cpp
index b75aad554..73da13b4c 100644
--- a/twml/libtwml/src/lib/BlockFormatWriter.cpp
+++ b/twml/libtwml/src/lib/BlockFormatWriter.cpp
@@ -11,7 +11,7 @@
 #endif
 
 #define MARKER_SIZE (16)
-static uint8_t _marker[MARKER_SIZE] = {
+static std::uint8_t _marker[MARKER_SIZE] = {
         0x29, 0xd8, 0xd5, 0x06, 0x58, 0xcd, 0x4c, 0x29,
         0xb2, 0xbc, 0x57, 0x99, 0x21, 0x71, 0xbd, 0xff
 };
@@ -21,10 +21,13 @@ namespace twml {
       file_name_(file_name), record_index_(0), records_per_block_(record_per_block) {
       snprintf(temp_file_name_, PATH_MAX, "%s.block", file_name);
       std::fstream outputfile_(file_name_, std::ios::app);
+      if (!outputfile_.is_open()) {
+        throw std::runtime_error("Failed to open the output file");
+      }
     }
 
-    int BlockFormatWriter::pack_tag_and_wiretype(std::fstream& fs, uint32_t tag, uint32_t wiretype) {
-      uint8_t x = ((tag & 0x0f) << 3) | (wiretype & 0x7);
+    int BlockFormatWriter::pack_tag_and_wiretype(std::fstream& fs, std::uint32_t tag, std::uint32_t wiretype) {
+      std::uint8_t x = ((tag & 0x0f) << 3) | (wiretype & 0x7);
       fs.write(reinterpret_cast<char*>(&x), sizeof(x));
       if (fs.fail()) {
         return -1;
@@ -34,10 +37,10 @@ namespace twml {
 
     int BlockFormatWriter::pack_varint_i32(std::fstream& fs, int value) {
       for (int i = 0; i < 10; i++) {
-        uint8_t x = value & 0x7F;
+        std::uint8_t x = value & 0x7F;
         value = value >> 7;
         if (value != 0) x |= 0x80;
-        fs.write(reinterpret_cast<char*>(&x), sizeof(x));
+        fs.write(reinterpret_cast<const char*>(&x), sizeof(x));
         if (fs.fail()) {
           return -1;
         }
@@ -56,11 +59,11 @@ namespace twml {
     }
 
     int BlockFormatWriter::write_int(std::fstream& fs, int value) {
-      uint8_t buff[4];
-      buff[0] = value & 0xff;
-      buff[1] = (value >> 8) & 0xff;
-      buff[2] = (value >> 16) & 0xff;
-      buff[3] = (value >> 24) & 0xff;
+      std::uint8_t buff[4];
+      buff[0] = static_cast<std::uint8_t>(value & 0xff);
+      buff[1] = static_cast<std::uint8_t>((value >> 8) & 0xff);
+      buff[2] = static_cast<std::uint8_t>((value >> 16) & 0xff);
+      buff[3] = static_cast<std::uint8_t>((value >> 24) & 0xff);
       fs.write(reinterpret_cast<char*>(buff), sizeof(buff));
       if (fs.fail()) {
         return -1;
@@ -73,7 +76,7 @@ namespace twml {
         record_index_++;
         // The buffer holds max records_per_block_ of records (block).
         std::fstream buffer(temp_file_name_, std::ios::app);
-        if (!buffer) return -1;
+        if (!buffer.is_open()) return -1;
         if (buffer.tellg() == 0) {
           if (pack_tag_and_wiretype(buffer, 1, WIRE_TYPE_VARINT))
             throw std::invalid_argument("Error writting tag and wiretype");
@@ -106,12 +109,12 @@ namespace twml {
 
         if (outputfile_.write(reinterpret_cast<const char*>(_marker), sizeof(_marker)).fail() != 1) return 1;
         if (write_int(outputfile_, block_size)) return 1;
-        uint8_t buff[4096];
+        std::uint8_t buff[4096];
         while (1) {
           buffer.read(reinterpret_cast<char*>(buff), sizeof(buff));
           std::streamsize n = buffer.gcount();
           if (n) {
-            outputfile_.write(reinterpret_cast<char*>(buff), n);
+            outputfile_.write(reinterpret_cast<const char*>(buff), n);
             if (outputfile_.fail()) return 1;
           }
           if (n != sizeof(buff)) break;