diff --git a/buffet/commands/cloud_command_proxy.cc b/buffet/commands/cloud_command_proxy.cc
index 341401e..4463c50 100644
--- a/buffet/commands/cloud_command_proxy.cc
+++ b/buffet/commands/cloud_command_proxy.cc
@@ -35,7 +35,8 @@
 
 void CloudCommandProxy::OnProgressChanged(int progress) {
   base::DictionaryValue patch;
-  patch.SetInteger(commands::attributes::kCommand_Progress, progress);
+  patch.Set(commands::attributes::kCommand_Progress,
+            command_instance_->GetProgressJson().release());
   // TODO(antonm): Consider batching progress change updates.
   device_registration_info_->UpdateCommand(command_instance_->GetID(), patch);
 }
diff --git a/buffet/commands/command_instance.cc b/buffet/commands/command_instance.cc
index c12f1ed..c67411f 100644
--- a/buffet/commands/command_instance.cc
+++ b/buffet/commands/command_instance.cc
@@ -152,7 +152,8 @@
             TypedValueToJson(parameters_, nullptr).release());
   json->Set(commands::attributes::kCommand_Results,
             TypedValueToJson(results_, nullptr).release());
-  json->SetInteger(commands::attributes::kCommand_Progress, progress_);
+  json->Set(commands::attributes::kCommand_Progress,
+            GetProgressJson().release());
   json->SetString(commands::attributes::kCommand_State, status_);
 
   return json;
@@ -219,5 +220,15 @@
     queue_->DelayedRemove(GetID());
 }
 
+std::unique_ptr<base::Value> CommandInstance::GetProgressJson() const {
+  // GCD server requires "progress" to be a JSON object. We will just make
+  // an object with a single field, "progress", so the patch request will
+  // look like this: {"progress": {"progress":100}}.
+  std::unique_ptr<base::DictionaryValue> progress_object{
+      new base::DictionaryValue};
+  progress_object->SetInteger(commands::attributes::kCommand_Progress,
+                              progress_);
+  return std::move(progress_object);
+}
 
 }  // namespace buffet
diff --git a/buffet/commands/command_instance.h b/buffet/commands/command_instance.h
index 2b09829..e5e0f9f 100644
--- a/buffet/commands/command_instance.h
+++ b/buffet/commands/command_instance.h
@@ -95,6 +95,9 @@
   int GetProgress() const { return progress_; }
   const std::string& GetStatus() const { return status_; }
 
+  // Returns the "progress" portion of JSON command resource.
+  std::unique_ptr<base::Value> GetProgressJson() const;
+
   // Values for command execution status.
   static const char kStatusQueued[];
   static const char kStatusInProgress[];
diff --git a/buffet/commands/command_instance_unittest.cc b/buffet/commands/command_instance_unittest.cc
index 48d54b9..e1d874b 100644
--- a/buffet/commands/command_instance_unittest.cc
+++ b/buffet/commands/command_instance_unittest.cc
@@ -209,7 +209,7 @@
 
   json->MergeDictionary(CreateDictionaryValue(R"({
     'id': 'testId',
-    'progress': 15,
+    'progress': {'progress': 15},
     'state': 'inProgress',
     'results': {'testResult': 17}
   })").get());
diff --git a/buffet/device_registration_info_unittest.cc b/buffet/device_registration_info_unittest.cc
index e3fb737..c800052 100644
--- a/buffet/device_registration_info_unittest.cc
+++ b/buffet/device_registration_info_unittest.cc
@@ -521,6 +521,8 @@
   })");
   EXPECT_TRUE(command_manager_->LoadCommands(*json_cmds, "", nullptr));
 
+  const std::string command_url = dev_reg_->GetServiceURL("commands/1234");
+
   auto commands_json = buffet::unittests::CreateValue(R"([{
     'name':'robot._jump',
     'id':'1234',
@@ -538,22 +540,50 @@
     {"status", string_type.CreateValue(std::string{"Ok"}, nullptr)}
   };
 
-  auto update_command = [](const ServerRequest& request,
-                           ServerResponse* response) {
-    // Make sure we serialize the JSON back without any pretty print so
-    // the string comparison works correctly.
-    auto json = request.GetDataAsJson();
-    EXPECT_NE(nullptr, json.get());
-    std::string value;
-    ASSERT_TRUE(base::JSONWriter::Write(json.get(), &value));
-    EXPECT_EQ(R"({"results":{"status":"Ok"}})", value);
+  // UpdateCommand when setting command results.
+  auto update_command_results = [](const ServerRequest& request,
+                                   ServerResponse* response) {
+    EXPECT_EQ(R"({"results":{"status":"Ok"}})",
+              request.GetDataAsNormalizedJsonString());
   };
 
-  transport_->AddHandler(dev_reg_->GetServiceURL("commands/1234"),
-      chromeos::http::request_type::kPatch,
-      base::Bind(update_command));
+  transport_->AddHandler(command_url,
+                         chromeos::http::request_type::kPatch,
+                         base::Bind(update_command_results));
 
   command->SetResults(results);
+
+  // UpdateCommand when setting command progress.
+  int count = 0;  // This will be called twice...
+  auto update_command_progress = [&count](const ServerRequest& request,
+                                          ServerResponse* response) {
+    if (count++ == 0) {
+      EXPECT_EQ(R"({"state":"inProgress"})",
+                request.GetDataAsNormalizedJsonString());
+    } else {
+      EXPECT_EQ(R"({"progress":{"progress":18}})",
+                request.GetDataAsNormalizedJsonString());
+    }
+  };
+
+  transport_->AddHandler(command_url,
+                         chromeos::http::request_type::kPatch,
+                         base::Bind(update_command_progress));
+
+  command->SetProgress(18);
+
+  // UpdateCommand when changing command status.
+  auto update_command_state = [](const ServerRequest& request,
+                                 ServerResponse* response) {
+    EXPECT_EQ(R"({"state":"cancelled"})",
+              request.GetDataAsNormalizedJsonString());
+  };
+
+  transport_->AddHandler(command_url,
+                         chromeos::http::request_type::kPatch,
+                         base::Bind(update_command_state));
+
+  command->Cancel();
 }