diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index a7966c7fb1d..f68063ad946 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -18569,11 +18569,18 @@ const char* UnhandledException::ToErrorCString() const {
     }
   }
   const Instance& stack = Instance::Handle(stacktrace());
-  strtmp = DartLibraryCalls::ToString(stack);
-  const char* stack_str =
-      "<Received error while converting stack trace to string>";
-  if (!strtmp.IsError()) {
-    stack_str = strtmp.ToCString();
+  const char* stack_str;
+  if (stack.IsNull()) {
+    stack_str = "null";
+  } else if (stack.IsStackTrace()) {
+    stack_str = StackTrace::Cast(stack).ToCString();
+  } else {
+    strtmp = DartLibraryCalls::ToString(stack);
+    if (!strtmp.IsError()) {
+      stack_str = strtmp.ToCString();
+    } else {
+      stack_str = "<Received error while converting stack trace to string>";
+    }
   }
   return OS::SCreate(thread->zone(), "Unhandled exception:\n%s\n%s", exc_str,
                      stack_str);
diff --git a/runtime/vm/service_isolate.cc b/runtime/vm/service_isolate.cc
index f2a12867efb..b8b855d611a 100644
--- a/runtime/vm/service_isolate.cc
+++ b/runtime/vm/service_isolate.cc
@@ -49,19 +49,40 @@ DEFINE_FLAG(bool,
 
 #define VM_SERVICE_METHOD_CALL_FROM_NATIVE 5
 
-static ArrayPtr MakeServiceControlMessage(Dart_Port port_id,
-                                          intptr_t code,
-                                          const String& name) {
-  const Array& list = Array::Handle(Array::New(4));
-  ASSERT(!list.IsNull());
-  const Integer& code_int = Integer::Handle(Integer::New(code));
-  const Integer& port_int = Integer::Handle(Integer::New(port_id));
-  const SendPort& send_port = SendPort::Handle(SendPort::New(port_id));
-  list.SetAt(0, code_int);
-  list.SetAt(1, port_int);
-  list.SetAt(2, send_port);
-  list.SetAt(3, name);
-  return list.ptr();
+bool ServiceIsolate::SendServiceControlMessage(Thread* thread,
+                                               Dart_Port port_id,
+                                               intptr_t code,
+                                               const char* name) {
+  Dart_CObject ccode;
+  ccode.type = Dart_CObject_kInt32;
+  ccode.value.as_int32 = code;
+
+  Dart_CObject port_int;
+  port_int.type = Dart_CObject_kInt64;
+  port_int.value.as_int64 = port_id;
+
+  Dart_CObject send_port;
+  send_port.type = Dart_CObject_kSendPort;
+  send_port.value.as_send_port.id = port_id;
+  send_port.value.as_send_port.origin_id = port_id;
+
+  Dart_CObject cname;
+  cname.type = Dart_CObject_kString;
+  cname.value.as_string = const_cast<char*>(name);
+
+  Dart_CObject* values[4];
+  values[0] = &ccode;
+  values[1] = &port_int;
+  values[2] = &send_port;
+  values[3] = &cname;
+
+  Dart_CObject message;
+  message.type = Dart_CObject_kArray;
+  message.value.as_array.length = 4;
+  message.value.as_array.values = values;
+
+  return PortMap::PostMessage(WriteApiMessage(thread->zone(), &message, port_,
+                                              Message::kNormalPriority));
 }
 
 static ArrayPtr MakeServerControlMessage(const SendPort& sp,
@@ -217,21 +238,16 @@ bool ServiceIsolate::SendIsolateStartupMessage() {
   if (Dart::VmIsolateNameEquals(isolate->name())) {
     return false;
   }
-  ASSERT(isolate != NULL);
-  HANDLESCOPE(thread);
-  const String& name = String::Handle(String::New(isolate->name()));
-  ASSERT(!name.IsNull());
-  const Array& list = Array::Handle(MakeServiceControlMessage(
-      Dart_GetMainPortId(), VM_SERVICE_ISOLATE_STARTUP_MESSAGE_ID, name));
-  ASSERT(!list.IsNull());
+
+  Dart_Port main_port = Dart_GetMainPortId();
   if (FLAG_trace_service) {
     OS::PrintErr(DART_VM_SERVICE_ISOLATE_NAME ": Isolate %s %" Pd64
                                               " registered.\n",
-                 name.ToCString(), Dart_GetMainPortId());
+                 isolate->name(), main_port);
   }
-  bool result = PortMap::PostMessage(WriteMessage(
-      /* can_send_any_object */ false, /* same_group */ false, list, port_,
-      Message::kNormalPriority));
+  bool result = SendServiceControlMessage(thread, main_port,
+                                          VM_SERVICE_ISOLATE_STARTUP_MESSAGE_ID,
+                                          isolate->name());
   isolate->set_is_service_registered(true);
   return result;
 }
@@ -245,21 +261,17 @@ bool ServiceIsolate::SendIsolateShutdownMessage() {
   if (Dart::VmIsolateNameEquals(isolate->name())) {
     return false;
   }
-  ASSERT(isolate != NULL);
-  HANDLESCOPE(thread);
-  const String& name = String::Handle(String::New(isolate->name()));
-  ASSERT(!name.IsNull());
-  const Array& list = Array::Handle(MakeServiceControlMessage(
-      Dart_GetMainPortId(), VM_SERVICE_ISOLATE_SHUTDOWN_MESSAGE_ID, name));
-  ASSERT(!list.IsNull());
+
+  Dart_Port main_port = Dart_GetMainPortId();
   if (FLAG_trace_service) {
     OS::PrintErr(DART_VM_SERVICE_ISOLATE_NAME ": Isolate %s %" Pd64
                                               " deregistered.\n",
-                 name.ToCString(), Dart_GetMainPortId());
+                 isolate->name(), main_port);
   }
-  return PortMap::PostMessage(WriteMessage(
-      /* can_send_any_object */ false, /* same_group */ false, list, port_,
-      Message::kNormalPriority));
+
+  return SendServiceControlMessage(thread, main_port,
+                                   VM_SERVICE_ISOLATE_SHUTDOWN_MESSAGE_ID,
+                                   isolate->name());
 }
 
 void ServiceIsolate::SendServiceExitMessage() {
diff --git a/runtime/vm/service_isolate.h b/runtime/vm/service_isolate.h
index 0fc018a9139..4dff10076d7 100644
--- a/runtime/vm/service_isolate.h
+++ b/runtime/vm/service_isolate.h
@@ -45,6 +45,10 @@ class ServiceIsolate : public AllStatic {
   static void Run();
   static bool SendIsolateStartupMessage();
   static bool SendIsolateShutdownMessage();
+  static bool SendServiceControlMessage(Thread* thread,
+                                        Dart_Port port_id,
+                                        intptr_t code,
+                                        const char* name);
   static void SendServiceExitMessage();
   static void Shutdown();