diff --git a/ReactCommon/react/renderer/mapbuffer/MapBuffer.cpp b/ReactCommon/react/renderer/mapbuffer/MapBuffer.cpp
index 3f3a6de85214e9..94d8c87bd323a4 100644
--- a/ReactCommon/react/renderer/mapbuffer/MapBuffer.cpp
+++ b/ReactCommon/react/renderer/mapbuffer/MapBuffer.cpp
@@ -33,11 +33,11 @@ MapBuffer::MapBuffer(std::vector<uint8_t> data) : bytes_(std::move(data)) {
   }
 }
 
-uint32_t MapBuffer::getKeyBucket(Key key) const {
-  uint32_t lo = 0;
-  uint32_t hi = count_ - 1;
+int32_t MapBuffer::getKeyBucket(Key key) const {
+  int32_t lo = 0;
+  int32_t hi = count_ - 1;
   while (lo <= hi) {
-    uint32_t mid = (lo + hi) >> 1;
+    int32_t mid = (lo + hi) >> 1;
 
     Key midVal =
         *reinterpret_cast<Key const *>(bytes_.data() + bucketOffset(mid));
@@ -112,7 +112,7 @@ MapBuffer MapBuffer::getMapBuffer(Key key) const {
   return MapBuffer(std::move(value));
 }
 
-uint32_t MapBuffer::size() const {
+size_t MapBuffer::size() const {
   return bytes_.size();
 }
 
diff --git a/ReactCommon/react/renderer/mapbuffer/MapBuffer.h b/ReactCommon/react/renderer/mapbuffer/MapBuffer.h
index 037e3e8ae34a34..fe683058512381 100644
--- a/ReactCommon/react/renderer/mapbuffer/MapBuffer.h
+++ b/ReactCommon/react/renderer/mapbuffer/MapBuffer.h
@@ -80,7 +80,8 @@ class MapBuffer {
     uint32_t bufferSize; // Amount of bytes used to store the map in memory
   };
 
-  struct __attribute__((__packed__)) Bucket {
+#pragma pack(push, 1)
+  struct Bucket {
     Key key;
     uint16_t type;
     uint64_t data;
@@ -88,6 +89,7 @@ class MapBuffer {
     Bucket(Key key, uint16_t type, uint64_t data)
         : key(key), type(type), data(data) {}
   };
+#pragma pack(pop)
 
   static_assert(sizeof(Header) == 8, "MapBuffer header size is incorrect.");
   static_assert(sizeof(Bucket) == 12, "MapBuffer bucket size is incorrect.");
@@ -124,7 +126,7 @@ class MapBuffer {
   // TODO T83483191: review this declaration
   MapBuffer getMapBuffer(MapBuffer::Key key) const;
 
-  uint32_t size() const;
+  size_t size() const;
 
   uint8_t const *data() const;
 
@@ -140,7 +142,7 @@ class MapBuffer {
   // returns the relative offset of the first byte of dynamic data
   int32_t getDynamicDataOffset() const;
 
-  uint32_t getKeyBucket(MapBuffer::Key key) const;
+  int32_t getKeyBucket(MapBuffer::Key key) const;
 
   friend ReadableMapBuffer;
 };
diff --git a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
index 3d06fba880a15d..93883437012bc3 100644
--- a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
+++ b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp
@@ -14,7 +14,7 @@ namespace facebook {
 namespace react {
 
 constexpr uint32_t INT_SIZE = sizeof(uint32_t);
-constexpr double DOUBLE_SIZE = sizeof(double);
+constexpr uint32_t DOUBLE_SIZE = sizeof(double);
 constexpr uint32_t MAX_BUCKET_VALUE_SIZE = sizeof(uint64_t);
 
 MapBuffer MapBufferBuilder::EMPTY() {
@@ -23,6 +23,8 @@ MapBuffer MapBufferBuilder::EMPTY() {
 
 MapBufferBuilder::MapBufferBuilder(uint32_t initialSize) {
   buckets_.reserve(initialSize);
+  header_.count = 0;
+  header_.bufferSize = 0;
 }
 
 void MapBufferBuilder::storeKeyValue(
@@ -76,7 +78,7 @@ void MapBufferBuilder::putInt(MapBuffer::Key key, int32_t value) {
 }
 
 void MapBufferBuilder::putString(MapBuffer::Key key, std::string const &value) {
-  int32_t strSize = value.size();
+  auto strSize = value.size();
   const char *strData = value.data();
 
   // format [length of string (int)] + [Array of Characters in the string]
@@ -94,7 +96,7 @@ void MapBufferBuilder::putString(MapBuffer::Key key, std::string const &value) {
 }
 
 void MapBufferBuilder::putMapBuffer(MapBuffer::Key key, MapBuffer const &map) {
-  int32_t mapBufferSize = map.size();
+  auto mapBufferSize = map.size();
 
   auto offset = dynamicData_.size();
 
@@ -122,9 +124,9 @@ MapBuffer MapBufferBuilder::build() {
   // Create buffer: [header] + [key, values] + [dynamic data]
   auto bucketSize = buckets_.size() * sizeof(MapBuffer::Bucket);
   auto headerSize = sizeof(MapBuffer::Header);
-  uint32_t bufferSize = headerSize + bucketSize + dynamicData_.size();
+  auto bufferSize = headerSize + bucketSize + dynamicData_.size();
 
-  header_.bufferSize = bufferSize;
+  header_.bufferSize = static_cast<uint32_t>(bufferSize);
 
   if (needsSort_) {
     std::sort(buckets_.begin(), buckets_.end(), compareBuckets);
diff --git a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.h b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.h
index 154c5daa63d722..aa8ae879407487 100644
--- a/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.h
+++ b/ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.h
@@ -38,7 +38,7 @@ class MapBufferBuilder {
   MapBuffer build();
 
  private:
-  MapBuffer::Header header_ = {.count = 0, .bufferSize = 0};
+  MapBuffer::Header header_;
 
   std::vector<MapBuffer::Bucket> buckets_{};