diff --git a/src/anbox/rpc/channel.cpp b/src/anbox/rpc/channel.cpp
index 71ffa80..b0c2ead 100644
--- a/src/anbox/rpc/channel.cpp
+++ b/src/anbox/rpc/channel.cpp
@@ -74,6 +74,7 @@ void Channel::send_message(const std::uint8_t &type,
                            google::protobuf::MessageLite const &message) {
   const size_t size = message.ByteSize();
   const unsigned char header_bytes[header_size] = {
+      static_cast<unsigned char>((size >>16) & 0xff),
       static_cast<unsigned char>((size >> 8) & 0xff),
       static_cast<unsigned char>((size >> 0) & 0xff), type,
   };
diff --git a/src/anbox/rpc/constants.h b/src/anbox/rpc/constants.h
index 1d4265a..4f5d04a 100644
--- a/src/anbox/rpc/constants.h
+++ b/src/anbox/rpc/constants.h
@@ -20,7 +20,7 @@
 
 namespace anbox {
 namespace rpc {
-static constexpr const long header_size{3};
+static constexpr const long header_size{4};
 static constexpr unsigned int const serialization_buffer_size{2048};
 
 enum MessageType {
diff --git a/src/anbox/rpc/message_processor.cpp b/src/anbox/rpc/message_processor.cpp
index 90e70ef..ba25a5a 100644
--- a/src/anbox/rpc/message_processor.cpp
+++ b/src/anbox/rpc/message_processor.cpp
@@ -47,9 +47,10 @@ bool MessageProcessor::process_data(const std::vector<std::uint8_t> &data) {
 
   while (buffer_.size() > 0) {
     const auto high = buffer_[0];
-    const auto low = buffer_[1];
-    size_t const message_size = (high << 8) + low;
-    const auto message_type = buffer_[2];
+    const auto medium = buffer_[1];
+    const auto low = buffer_[2];
+    size_t const message_size = (high << 16) + (medium << 8) + low;
+    const auto message_type = buffer_[3];
 
     // If we don't have yet all bytes for a new message return and wait
     // until we have all.
@@ -101,6 +102,7 @@ void MessageProcessor::send_response(::google::protobuf::uint32 id,
 
   const size_t size = send_response_buffer.size();
   const unsigned char header_bytes[header_size] = {
+      static_cast<unsigned char>((size >> 16) & 0xff),
       static_cast<unsigned char>((size >> 8) & 0xff),
       static_cast<unsigned char>((size >> 0) & 0xff), MessageType::response,
   };