diff --git a/trunks/trunks_binder_proxy.cc b/trunks/trunks_binder_proxy.cc
index 772afc7..ed1052a 100644
--- a/trunks/trunks_binder_proxy.cc
+++ b/trunks/trunks_binder_proxy.cc
@@ -38,7 +38,7 @@
 
   // ITrunksClient interface.
   android::binder::Status OnCommandResponse(
-      const std::vector<int8_t>& response_proto_data) override {
+      const std::vector<uint8_t>& response_proto_data) override {
     trunks::SendCommandResponse response_proto;
     if (!response_proto.ParseFromArray(response_proto_data.data(),
                                        response_proto_data.size())) {
@@ -74,7 +74,7 @@
                                     const ResponseCallback& callback) {
   SendCommandRequest command_proto;
   command_proto.set_command(command);
-  std::vector<int8_t> command_proto_data;
+  std::vector<uint8_t> command_proto_data;
   command_proto_data.resize(command_proto.ByteSize());
   if (!command_proto.SerializeToArray(command_proto_data.data(),
                                       command_proto_data.size())) {
@@ -95,14 +95,14 @@
 std::string TrunksBinderProxy::SendCommandAndWait(const std::string& command) {
   SendCommandRequest command_proto;
   command_proto.set_command(command);
-  std::vector<int8_t> command_proto_data;
+  std::vector<uint8_t> command_proto_data;
   command_proto_data.resize(command_proto.ByteSize());
   if (!command_proto.SerializeToArray(command_proto_data.data(),
                                       command_proto_data.size())) {
     LOG(ERROR) << "TrunksBinderProxy: Failed to serialize protobuf.";
     return CreateErrorResponse(TRUNKS_RC_IPC_ERROR);
   }
-  std::vector<int8_t> response_proto_data;
+  std::vector<uint8_t> response_proto_data;
   android::binder::Status status = trunks_service_->SendCommandAndWait(
       command_proto_data, &response_proto_data);
   if (!status.isOk()) {
diff --git a/trunks/trunks_binder_service.cc b/trunks/trunks_binder_service.cc
index 028aa3c..b8b72b5 100644
--- a/trunks/trunks_binder_service.cc
+++ b/trunks/trunks_binder_service.cc
@@ -30,7 +30,7 @@
 
 // If |command| is a valid command protobuf, provides the |command_data| and
 // returns true. Otherwise, returns false.
-bool ParseCommandProto(const std::vector<int8_t>& command,
+bool ParseCommandProto(const std::vector<uint8_t>& command,
                        std::string* command_data) {
   trunks::SendCommandRequest request_proto;
   if (!request_proto.ParseFromArray(command.data(), command.size()) ||
@@ -42,7 +42,7 @@
 }
 
 void CreateResponseProto(const std::string& data,
-                         std::vector<int8_t>* response) {
+                         std::vector<uint8_t>* response) {
   trunks::SendCommandResponse response_proto;
   response_proto.set_response(data);
   response->resize(response_proto.ByteSize());
@@ -75,7 +75,7 @@
     : service_(service) {}
 
 android::binder::Status TrunksBinderService::BinderServiceInternal::SendCommand(
-    const std::vector<int8_t>& command,
+    const std::vector<uint8_t>& command,
     const android::sp<android::trunks::ITrunksClient>& client) {
   auto callback =
       base::Bind(&TrunksBinderService::BinderServiceInternal::OnResponse,
@@ -93,7 +93,7 @@
 void TrunksBinderService::BinderServiceInternal::OnResponse(
     const android::sp<android::trunks::ITrunksClient>& client,
     const std::string& response) {
-  std::vector<int8_t> binder_response;
+  std::vector<uint8_t> binder_response;
   CreateResponseProto(response, &binder_response);
   android::binder::Status status = client->OnCommandResponse(binder_response);
   if (!status.isOk()) {
@@ -104,8 +104,8 @@
 
 android::binder::Status
 TrunksBinderService::BinderServiceInternal::SendCommandAndWait(
-    const std::vector<int8_t>& command,
-    std::vector<int8_t>* response) {
+    const std::vector<uint8_t>& command,
+    std::vector<uint8_t>* response) {
   std::string command_data;
   if (!ParseCommandProto(command, &command_data)) {
     LOG(ERROR) << "TrunksBinderService: Bad command data.";
diff --git a/trunks/trunks_binder_service.h b/trunks/trunks_binder_service.h
index 7f809ac..0352b74 100644
--- a/trunks/trunks_binder_service.h
+++ b/trunks/trunks_binder_service.h
@@ -57,11 +57,11 @@
 
     // ITrunks interface.
     android::binder::Status SendCommand(
-        const std::vector<int8_t>& command,
+        const std::vector<uint8_t>& command,
         const android::sp<android::trunks::ITrunksClient>& client) override;
     android::binder::Status SendCommandAndWait(
-        const std::vector<int8_t>& command,
-        std::vector<int8_t>* response) override;
+        const std::vector<uint8_t>& command,
+        std::vector<uint8_t>* response) override;
 
    private:
     void OnResponse(const android::sp<android::trunks::ITrunksClient>& client,