diff --git a/sandboxed_api/call.h b/sandboxed_api/call.h
index a33306a..06def7e 100644
--- a/sandboxed_api/call.h
+++ b/sandboxed_api/call.h
@@ -23,8 +23,8 @@ namespace sapi {
 namespace comms {
 
 struct ReallocRequest {
-  uint64_t old_addr;
-  uint64_t size;
+  uintptr_t old_addr;
+  size_t size;
 };
 
 // Types of TAGs used with Comms channel.
diff --git a/sandboxed_api/client.cc b/sandboxed_api/client.cc
index 738fc87..9d490b6 100644
--- a/sandboxed_api/client.cc
+++ b/sandboxed_api/client.cc
@@ -229,7 +229,7 @@ void HandleCallMsg(const FuncCall& call, FuncRet* ret) {
 }
 
 // Handles requests to allocate memory inside the sandboxee.
-void HandleAllocMsg(const uintptr_t size, FuncRet* ret) {
+void HandleAllocMsg(const size_t size, FuncRet* ret) {
   VLOG(1) << "HandleAllocMsg: size=" << size;
 
   ret->ret_type = v::Type::kPointer;
@@ -237,16 +237,15 @@ void HandleAllocMsg(const uintptr_t size, FuncRet* ret) {
   // Memory is copied to the pointer using an API that the memory sanitizer
   // is blind to (process_vm_writev). Initialize the memory here so that
   // the sandboxed code can still be tested with the memory sanitizer.
-  ret->int_val =
-      reinterpret_cast<uintptr_t>(calloc(1, static_cast<size_t>(size)));
+  ret->int_val = reinterpret_cast<uintptr_t>(calloc(1, size));
 #else
-  ret->int_val = reinterpret_cast<uintptr_t>(malloc(static_cast<size_t>(size)));
+  ret->int_val = reinterpret_cast<uintptr_t>(malloc(size));
 #endif
   ret->success = true;
 }
 
 // Like HandleAllocMsg(), but handles requests to reallocate memory.
-void HandleReallocMsg(uintptr_t ptr, uintptr_t size, FuncRet* ret) {
+void HandleReallocMsg(uintptr_t ptr, size_t size, FuncRet* ret) {
   VLOG(1) << "HandleReallocMsg(" << absl::StrCat(absl::Hex(ptr)) << ", " << size
           << ")";
 #ifdef MEMORY_SANITIZER
@@ -363,14 +362,13 @@ void ServeRequest(sandbox2::Comms* comms) {
       break;
     case comms::kMsgAllocate:
       VLOG(1) << "Client::kMsgAllocate";
-      HandleAllocMsg(BytesAs<uintptr_t>(bytes), &ret);
+      HandleAllocMsg(BytesAs<size_t>(bytes), &ret);
       break;
     case comms::kMsgReallocate:
       VLOG(1) << "Client::kMsgReallocate";
       {
         auto req = BytesAs<comms::ReallocRequest>(bytes);
-        HandleReallocMsg(static_cast<uintptr_t>(req.old_addr),
-                         static_cast<uintptr_t>(req.size), &ret);
+        HandleReallocMsg(req.old_addr, req.size, &ret);
       }
       break;
     case comms::kMsgFree:
diff --git a/sandboxed_api/examples/stringop/main_stringop.cc b/sandboxed_api/examples/stringop/main_stringop.cc
index 9880699..c7e5b2e 100644
--- a/sandboxed_api/examples/stringop/main_stringop.cc
+++ b/sandboxed_api/examples/stringop/main_stringop.cc
@@ -134,7 +134,7 @@ TEST(StringopTest, RawStringLength) {
   ASSERT_THAT(sandbox.Init(), IsOk());
   StringopApi api(&sandbox);
   SAPI_ASSERT_OK_AND_ASSIGN(void* target_mem_ptr, api.get_raw_c_string());
-  SAPI_ASSERT_OK_AND_ASSIGN(uint64_t len,
+  SAPI_ASSERT_OK_AND_ASSIGN(size_t len,
                        sandbox.rpc_channel()->Strlen(target_mem_ptr));
   EXPECT_THAT(len, Eq(10));
 }
@@ -144,7 +144,7 @@ TEST(StringopTest, RawStringReading) {
   ASSERT_THAT(sandbox.Init(), IsOk());
   StringopApi api(&sandbox);
   SAPI_ASSERT_OK_AND_ASSIGN(void* target_mem_ptr, api.get_raw_c_string());
-  SAPI_ASSERT_OK_AND_ASSIGN(uint64_t len,
+  SAPI_ASSERT_OK_AND_ASSIGN(size_t len,
                        sandbox.rpc_channel()->Strlen(target_mem_ptr));
   EXPECT_THAT(len, Eq(10));
 
diff --git a/sandboxed_api/rpcchannel.cc b/sandboxed_api/rpcchannel.cc
index 8b19547..72a057e 100644
--- a/sandboxed_api/rpcchannel.cc
+++ b/sandboxed_api/rpcchannel.cc
@@ -37,7 +37,7 @@ absl::Status RPCChannel::Call(const FuncCall& call, uint32_t tag, FuncRet* ret,
 
 absl::StatusOr<FuncRet> RPCChannel::Return(v::Type exp_type) {
   uint32_t tag;
-  uint64_t len;
+  size_t len;
   FuncRet ret;
   if (!comms_->RecvTLV(&tag, &len, &ret, sizeof(ret))) {
     return absl::UnavailableError("Receiving TLV value failed");
@@ -78,9 +78,10 @@ absl::Status RPCChannel::Allocate(size_t size, void** addr) {
 absl::Status RPCChannel::Reallocate(void* old_addr, size_t size,
                                     void** new_addr) {
   absl::MutexLock lock(&mutex_);
-  comms::ReallocRequest req;
-  req.old_addr = reinterpret_cast<uint64_t>(old_addr);
-  req.size = size;
+  comms::ReallocRequest req = {
+      .old_addr = reinterpret_cast<uintptr_t>(old_addr),
+      .size = size,
+  };
 
   if (!comms_->SendTLV(comms::kMsgReallocate, sizeof(comms::ReallocRequest),
                        &req)) {
@@ -100,7 +101,7 @@ absl::Status RPCChannel::Reallocate(void* old_addr, size_t size,
 
 absl::Status RPCChannel::Free(void* addr) {
   absl::MutexLock lock(&mutex_);
-  uint64_t remote = reinterpret_cast<uint64_t>(addr);
+  uintptr_t remote = reinterpret_cast<uintptr_t>(addr);
   if (!comms_->SendTLV(comms::kMsgFree, sizeof(remote), &remote)) {
     return absl::UnavailableError("Sending TLV value failed");
   }
@@ -193,7 +194,7 @@ absl::Status RPCChannel::Close(int remote_fd) {
   return absl::OkStatus();
 }
 
-absl::StatusOr<uint64_t> RPCChannel::Strlen(void* str) {
+absl::StatusOr<size_t> RPCChannel::Strlen(void* str) {
   absl::MutexLock lock(&mutex_);
   if (!comms_->SendTLV(comms::kMsgStrlen, sizeof(str), &str)) {
     return absl::UnavailableError("Sending TLV value failed");
diff --git a/sandboxed_api/rpcchannel.h b/sandboxed_api/rpcchannel.h
index 4fec23b..56d7ed8 100644
--- a/sandboxed_api/rpcchannel.h
+++ b/sandboxed_api/rpcchannel.h
@@ -61,7 +61,7 @@ class RPCChannel {
   absl::Status Close(int remote_fd);
 
   // Returns length of a null-terminated c-style string (invokes strlen).
-  absl::StatusOr<uint64_t> Strlen(void* str);
+  absl::StatusOr<size_t> Strlen(void* str);
 
   sandbox2::Comms* comms() const { return comms_; }
 
diff --git a/sandboxed_api/sandbox.cc b/sandboxed_api/sandbox.cc
index 8c9da3d..d6b1bf2 100644
--- a/sandboxed_api/sandbox.cc
+++ b/sandboxed_api/sandbox.cc
@@ -394,7 +394,7 @@ absl::Status Sandbox::TransferFromSandboxee(v::Var* var) {
 }
 
 absl::StatusOr<std::string> Sandbox::GetCString(const v::RemotePtr& str,
-                                                uint64_t max_length) {
+                                                size_t max_length) {
   if (!is_active()) {
     return absl::UnavailableError("Sandbox not active");
   }
diff --git a/sandboxed_api/sandbox.h b/sandboxed_api/sandbox.h
index 5d69eb0..576a144 100644
--- a/sandboxed_api/sandbox.h
+++ b/sandboxed_api/sandbox.h
@@ -103,8 +103,8 @@ class Sandbox {
   absl::Status TransferFromSandboxee(v::Var* var);
 
   absl::StatusOr<std::string> GetCString(const v::RemotePtr& str,
-                                         uint64_t max_length = 10ULL
-                                                               << 20 /* 10 MiB*/
+                                         size_t max_length = 10ULL
+                                                             << 20 /* 10 MiB*/
   );
 
   // Waits until the sandbox terminated and returns the result.
diff --git a/sandboxed_api/sandbox2/comms.cc b/sandboxed_api/sandbox2/comms.cc
index 9b2f719..449db8f 100644
--- a/sandboxed_api/sandbox2/comms.cc
+++ b/sandboxed_api/sandbox2/comms.cc
@@ -228,7 +228,7 @@ void Comms::Terminate() {
   }
 }
 
-bool Comms::SendTLV(uint32_t tag, uint64_t length, const void* value) {
+bool Comms::SendTLV(uint32_t tag, size_t length, const void* value) {
   if (length > GetMaxMsgSize()) {
     SAPI_RAW_LOG(ERROR, "Maximum TLV message size exceeded: (%u > %u)", length,
                  GetMaxMsgSize());
@@ -296,7 +296,7 @@ bool Comms::RecvBytes(std::vector<uint8_t>* buffer) {
   return true;
 }
 
-bool Comms::SendBytes(const uint8_t* v, uint64_t len) {
+bool Comms::SendBytes(const uint8_t* v, size_t len) {
   return SendTLV(kTagBytes, len, v);
 }
 
@@ -417,7 +417,7 @@ bool Comms::SendFD(int fd) {
   int* fds = reinterpret_cast<int*>(CMSG_DATA(cmsg));
   fds[0] = fd;
 
-  InternalTLV tlv = {kTagFd, sizeof(tlv.val), 0};
+  InternalTLV tlv = {kTagFd, 0};
 
   iovec iov;
   iov.iov_base = &tlv;
@@ -512,8 +512,8 @@ socklen_t Comms::CreateSockaddrUn(sockaddr_un* sun) {
   return slen;
 }
 
-bool Comms::Send(const void* data, uint64_t len) {
-  uint64_t total_sent = 0;
+bool Comms::Send(const void* data, size_t len) {
+  size_t total_sent = 0;
   const char* bytes = reinterpret_cast<const char*>(data);
   const auto op = [bytes, len, &total_sent](int fd) -> ssize_t {
     PotentiallyBlockingRegion region;
@@ -545,8 +545,8 @@ bool Comms::Send(const void* data, uint64_t len) {
   return true;
 }
 
-bool Comms::Recv(void* data, uint64_t len) {
-  uint64_t total_recv = 0;
+bool Comms::Recv(void* data, size_t len) {
+  size_t total_recv = 0;
   char* bytes = reinterpret_cast<char*>(data);
   const auto op = [bytes, len, &total_recv](int fd) -> ssize_t {
     PotentiallyBlockingRegion region;
@@ -574,7 +574,7 @@ bool Comms::Recv(void* data, uint64_t len) {
 }
 
 // Internal helper method (low level).
-bool Comms::RecvTL(uint32_t* tag, uint64_t* length) {
+bool Comms::RecvTL(uint32_t* tag, size_t* length) {
   if (!Recv(reinterpret_cast<uint8_t*>(tag), sizeof(*tag))) {
     return false;
   }
@@ -611,7 +611,7 @@ bool Comms::RecvTLV(uint32_t* tag, std::string* value) {
 template <typename T>
 bool Comms::RecvTLVGeneric(uint32_t* tag, T* value) {
   absl::MutexLock lock(&tlv_recv_transmission_mutex_);
-  uint64_t length;
+  size_t length;
   if (!RecvTL(tag, &length)) {
     return false;
   }
@@ -620,28 +620,29 @@ bool Comms::RecvTLVGeneric(uint32_t* tag, T* value) {
   return length == 0 || Recv(reinterpret_cast<uint8_t*>(value->data()), length);
 }
 
-bool Comms::RecvTLV(uint32_t* tag, uint64_t* length, void* buffer,
-                    uint64_t buffer_size) {
+bool Comms::RecvTLV(uint32_t* tag, size_t* length, void* buffer,
+                    size_t buffer_size) {
   absl::MutexLock lock(&tlv_recv_transmission_mutex_);
   if (!RecvTL(tag, length)) {
     return false;
   }
 
+  if (*length == 0) {
+    return true;
+  }
+
   if (*length > buffer_size) {
     SAPI_RAW_LOG(ERROR, "Buffer size too small (0x%x > 0x%x)", *length,
                  buffer_size);
     return false;
-  } else if (*length > 0) {
-    if (!Recv(reinterpret_cast<uint8_t*>(buffer), *length)) {
-      return false;
-    }
   }
-  return true;
+
+  return Recv(reinterpret_cast<uint8_t*>(buffer), *length);
 }
 
-bool Comms::RecvInt(void* buffer, uint64_t len, uint32_t tag) {
+bool Comms::RecvInt(void* buffer, size_t len, uint32_t tag) {
   uint32_t received_tag;
-  uint64_t received_length;
+  size_t received_length;
   if (!RecvTLV(&received_tag, &received_length, buffer, len)) {
     return false;
   }
diff --git a/sandboxed_api/sandbox2/comms.h b/sandboxed_api/sandbox2/comms.h
index 530943e..fca8c53 100644
--- a/sandboxed_api/sandbox2/comms.h
+++ b/sandboxed_api/sandbox2/comms.h
@@ -60,7 +60,7 @@ class Comms {
   static constexpr uint32_t kTagFd = 0X80000201;
 
   // Any payload size above this limit will LOG(WARNING).
-  static constexpr uint64_t kWarnMsgSize = (256ULL << 20);
+  static constexpr size_t kWarnMsgSize = (256ULL << 20);
 
   // Sandbox2-specific convention where FD=1023 is always passed to the
   // sandboxed process as a communication channel (encapsulated in the
@@ -103,9 +103,9 @@ class Comms {
   // Note: The actual size is "unlimited", although the Buffer API is more
   // efficient for large transfers. There is an arbitrary limit to ~2GiB to
   // avoid protobuf serialization issues.
-  uint64_t GetMaxMsgSize() const { return std::numeric_limits<int32_t>::max(); }
+  size_t GetMaxMsgSize() const { return std::numeric_limits<int32_t>::max(); }
 
-  bool SendTLV(uint32_t tag, uint64_t length, const void* value);
+  bool SendTLV(uint32_t tag, size_t length, const void* value);
   // Receive a TLV structure, the memory for the value will be allocated
   // by std::vector.
   bool RecvTLV(uint32_t* tag, std::vector<uint8_t>* value);
@@ -113,7 +113,7 @@ class Comms {
   // by std::string.
   bool RecvTLV(uint32_t* tag, std::string* value);
   // Receives a TLV value into a specified buffer without allocating memory.
-  bool RecvTLV(uint32_t* tag, uint64_t* length, void* buffer, uint64_t buffer_size);
+  bool RecvTLV(uint32_t* tag, size_t* length, void* buffer, size_t buffer_size);
 
   // Sends/receives various types of data.
   bool RecvUint8(uint8_t* v) { return RecvIntGeneric(v, kTagUint8); }
@@ -138,7 +138,7 @@ class Comms {
   bool SendString(const std::string& v);
 
   bool RecvBytes(std::vector<uint8_t>* buffer);
-  bool SendBytes(const uint8_t* v, uint64_t len);
+  bool SendBytes(const uint8_t* v, size_t len);
   bool SendBytes(const std::vector<uint8_t>& buffer);
 
   // Receives remote process credentials.
@@ -183,19 +183,18 @@ class Comms {
   struct ABSL_ATTRIBUTE_PACKED InternalTLV {
     uint32_t tag;
     uint32_t len;
-    uint64_t val;
   };
 
   // Fills sockaddr_un struct with proper values.
   socklen_t CreateSockaddrUn(sockaddr_un* sun);
 
   // Support for EINTR and size completion.
-  bool Send(const void* data, uint64_t len);
-  bool Recv(void* data, uint64_t len);
+  bool Send(const void* data, size_t len);
+  bool Recv(void* data, size_t len);
 
   // Receives tag and length. Assumes that the `tlv_transmission_mutex_` mutex
   // is locked.
-  bool RecvTL(uint32_t* tag, uint64_t* length)
+  bool RecvTL(uint32_t* tag, size_t* length)
       ABSL_EXCLUSIVE_LOCKS_REQUIRED(tlv_recv_transmission_mutex_);
 
   // T has to be a ContiguousContainer
@@ -203,7 +202,7 @@ class Comms {
   bool RecvTLVGeneric(uint32_t* tag, T* value);
 
   // Receives arbitrary integers.
-  bool RecvInt(void* buffer, uint64_t len, uint32_t tag);
+  bool RecvInt(void* buffer, size_t len, uint32_t tag);
 
   template <typename T>
   bool RecvIntGeneric(T* output, uint32_t tag) {