diff --git a/client_library/client_dbus.cc b/client_library/client_dbus.cc
index 48a563b..18ae23b 100644
--- a/client_library/client_dbus.cc
+++ b/client_library/client_dbus.cc
@@ -92,13 +92,8 @@
         dlc_parameters.add_dlc_module_infos();
     dlc_module_info->set_dlc_id(dlc_id);
   }
-  string dlc_request;
-  if (dlc_parameters.SerializeToString(&dlc_request)) {
-    return proxy_->AttemptInstall(dlc_request, nullptr /* brillo::ErrorPtr* */);
-  } else {
-    LOG(ERROR) << "Fail to serialize a protobuf to a string.";
-    return false;
-  }
+  return proxy_->AttemptInstall(dlc_parameters,
+                                nullptr /* brillo::ErrorPtr* */);
 }
 
 bool DBusUpdateEngineClient::GetStatus(int64_t* out_last_checked_time,
diff --git a/client_library/client_dbus.h b/client_library/client_dbus.h
index 1b127e3..c9631cf 100644
--- a/client_library/client_dbus.h
+++ b/client_library/client_dbus.h
@@ -23,6 +23,7 @@
 #include <vector>
 
 #include <base/macros.h>
+#include <dlcservice/proto_bindings/dlcservice.pb.h>
 #include <update_engine/proto_bindings/update_engine.pb.h>
 
 #include "update_engine/client_library/include/update_engine/client.h"
diff --git a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
index ef7bea7..a183147 100644
--- a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
+++ b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
@@ -35,7 +35,13 @@
       <arg type="i" name="flags" direction="in" />
     </method>
     <method name="AttemptInstall">
-      <arg type="s" name="dlc_request" direction="in" />
+      <arg type="ay" name="request" direction="in">
+        <tp:docstring>
+          The information about DLC modules that needs to be installed.
+        </tp:docstring>
+        <annotation name="org.chromium.DBus.Argument.ProtobufClass"
+                    value="dlcservice::DlcModuleList"/>
+      </arg>
     </method>
     <method name="AttemptRollback">
       <arg type="b" name="powerwash" direction="in" />
diff --git a/dbus_service.cc b/dbus_service.cc
index 105d581..4e37221 100644
--- a/dbus_service.cc
+++ b/dbus_service.cc
@@ -30,6 +30,7 @@
 
 using brillo::ErrorPtr;
 using chromeos_update_engine::UpdateEngineService;
+using dlcservice::DlcModuleList;
 using std::string;
 using std::vector;
 using update_engine::StatusResult;
@@ -77,25 +78,17 @@
 }
 
 bool DBusUpdateEngineService::AttemptInstall(ErrorPtr* error,
-                                             const string& dlc_request) {
-  // Parse the raw parameters into protobuf.
-  dlcservice::DlcModuleList dlc_parameters;
-  if (!dlc_parameters.ParseFromString(dlc_request)) {
-    *error = brillo::Error::Create(
-        FROM_HERE, "update_engine", "INTERNAL", "parameters are invalid.");
-    return false;
-  }
-  // Extract fields from the protobuf.
+                                             const DlcModuleList& request) {
   vector<string> dlc_ids;
-  for (const auto& dlc_module_info : dlc_parameters.dlc_module_infos()) {
+  for (const auto& dlc_module_info : request.dlc_module_infos()) {
     if (dlc_module_info.dlc_id().empty()) {
       *error = brillo::Error::Create(
-          FROM_HERE, "update_engine", "INTERNAL", "parameters are invalid.");
+          FROM_HERE, "update_engine", "INTERNAL", "Empty DLC ID passed.");
       return false;
     }
     dlc_ids.push_back(dlc_module_info.dlc_id());
   }
-  return common_->AttemptInstall(error, dlc_parameters.omaha_url(), dlc_ids);
+  return common_->AttemptInstall(error, request.omaha_url(), dlc_ids);
 }
 
 bool DBusUpdateEngineService::AttemptRollback(ErrorPtr* error,
diff --git a/dbus_service.h b/dbus_service.h
index 71a6d2b..2babf8c 100644
--- a/dbus_service.h
+++ b/dbus_service.h
@@ -24,6 +24,7 @@
 
 #include <base/memory/ref_counted.h>
 #include <brillo/errors/error.h>
+#include <dlcservice/proto_bindings/dlcservice.pb.h>
 #include <update_engine/proto_bindings/update_engine.pb.h>
 
 #include "update_engine/common_service.h"
@@ -51,7 +52,7 @@
                               int32_t in_flags_as_int) override;
 
   bool AttemptInstall(brillo::ErrorPtr* error,
-                      const std::string& dlc_request) override;
+                      const dlcservice::DlcModuleList& request) override;
 
   bool AttemptRollback(brillo::ErrorPtr* error, bool in_powerwash) override;
 
diff --git a/dlcservice_chromeos.cc b/dlcservice_chromeos.cc
index e95f08f..b7dee36 100644
--- a/dlcservice_chromeos.cc
+++ b/dlcservice_chromeos.cc
@@ -16,11 +16,13 @@
 
 #include "update_engine/dlcservice_chromeos.h"
 
-#include <dlcservice/dbus-proxies.h>
 #include <dlcservice/proto_bindings/dlcservice.pb.h>
+// NOLINTNEXTLINE(build/include_alpha) "dbus-proxies.h" needs "dlcservice.pb.h"
+#include <dlcservice/dbus-proxies.h>
 
 #include "update_engine/dbus_connection.h"
 
+using dlcservice::DlcModuleList;
 using std::string;
 using std::vector;
 
@@ -35,14 +37,10 @@
     return false;
   org::chromium::DlcServiceInterfaceProxy dlcservice_proxy(
       DBusConnection::Get()->GetDBus());
-  string dlc_module_list_str;
-  if (!dlcservice_proxy.GetInstalled(&dlc_module_list_str, nullptr)) {
-    LOG(ERROR) << "dlcservice does not return installed DLC module list.";
-    return false;
-  }
+
   dlcservice::DlcModuleList dlc_module_list;
-  if (!dlc_module_list.ParseFromString(dlc_module_list_str)) {
-    LOG(ERROR) << "Errors parsing DlcModuleList protobuf.";
+  if (!dlcservice_proxy.GetInstalled(&dlc_module_list, nullptr)) {
+    LOG(ERROR) << "dlcservice does not return installed DLC module list.";
     return false;
   }
   for (const auto& dlc_module_info : dlc_module_list.dlc_module_infos()) {