diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 4d4f0574a60..16f57fe65a0 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2099,8 +2099,8 @@ void Isolate::PrintJSON(JSONStream* stream, bool ref) {
   }
   JSONObject jsobj(stream);
   jsobj.AddProperty("type", (ref ? "@Isolate" : "Isolate"));
-  jsobj.AddFixedServiceId(ISOLATE_SERVICE_ID_FORMAT_STRING,
-                          static_cast<int64_t>(main_port()));
+  jsobj.AddServiceId(ISOLATE_SERVICE_ID_FORMAT_STRING,
+                     static_cast<int64_t>(main_port()));
 
   jsobj.AddProperty("name", name());
   jsobj.AddPropertyF("number", "%" Pd64 "", static_cast<int64_t>(main_port()));
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 05f474e43ab..1a78ed80453 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -500,6 +500,14 @@ void JSONObject::AddFixedServiceId(const char* format, ...) const {
   va_end(args);
 }
 
+void JSONObject::AddServiceId(const char* format, ...) const {
+  // Add the id property.
+  va_list args;
+  va_start(args, format);
+  stream_->VPrintfProperty("id", format, args);
+  va_end(args);
+}
+
 void JSONObject::AddLocation(const Script& script,
                              TokenPosition token_pos,
                              TokenPosition end_token_pos) const {
diff --git a/runtime/vm/json_stream.h b/runtime/vm/json_stream.h
index c44a5f615c2..98d39f3002d 100644
--- a/runtime/vm/json_stream.h
+++ b/runtime/vm/json_stream.h
@@ -307,6 +307,7 @@ class JSONObject : public ValueObject {
   void AddServiceId(const Object& o) const { stream_->PrintServiceId(o); }
 
   void AddFixedServiceId(const char* format, ...) const PRINTF_ATTRIBUTE(2, 3);
+  void AddServiceId(const char* format, ...) const PRINTF_ATTRIBUTE(2, 3);
 
   void AddLocation(
       const Script& script,