Index: ps/trunk/source/scriptinterface/ScriptInterface.cpp
===================================================================
--- ps/trunk/source/scriptinterface/ScriptInterface.cpp
+++ ps/trunk/source/scriptinterface/ScriptInterface.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -448,8 +448,11 @@
 		return;
 	}
 
-	JS::RootedObject ctorObj(rq.cx, &ctor.toObject());
-	out.setObjectOrNull(JS_New(rq.cx, ctorObj, argv));
+	JS::RootedObject objOut(rq.cx);
+	if (!JS::Construct(rq.cx, ctor, argv, &objOut))
+		out.setNull();
+	else
+		out.setObjectOrNull(objOut);
 }
 
 void ScriptInterface::DefineCustomObjectType(JSClass *clasp, JSNative constructor, uint minArgs, JSPropertySpec *ps, JSFunctionSpec *fs, JSPropertySpec *static_ps, JSFunctionSpec *static_fs)
Index: ps/trunk/source/simulation2/serialization/StdDeserializer.cpp
===================================================================
--- ps/trunk/source/simulation2/serialization/StdDeserializer.cpp
+++ ps/trunk/source/simulation2/serialization/StdDeserializer.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -278,9 +278,10 @@
 		JS::RootedObject ctorobj(rq.cx);
 		if (!JS_GetClassObject(rq.cx, JSProto_Number, &ctorobj))
 			throw PSERROR_Deserialize_ScriptError("JS_GetClassObject failed");
+		JS::RootedValue protoval(rq.cx, JS::ObjectOrNullValue(ctorobj));
 
-		JS::RootedObject obj(rq.cx, JS_New(rq.cx, ctorobj, JS::HandleValueArray(val)));
-		if (!obj)
+		JS::RootedObject obj(rq.cx);
+		if (!JS::Construct(rq.cx, protoval, JS::HandleValueArray(val), &obj))
 			throw PSERROR_Deserialize_ScriptError("JS_New failed");
 		AddScriptBackref(obj);
 		return JS::ObjectValue(*obj);
@@ -296,9 +297,10 @@
 		JS::RootedObject ctorobj(rq.cx);
 		if (!JS_GetClassObject(rq.cx, JSProto_String, &ctorobj))
 			throw PSERROR_Deserialize_ScriptError("JS_GetClassObject failed");
+		JS::RootedValue protoval(rq.cx, JS::ObjectOrNullValue(ctorobj));
 
-		JS::RootedObject obj(rq.cx, JS_New(rq.cx, ctorobj, JS::HandleValueArray(val)));
-		if (!obj)
+		JS::RootedObject obj(rq.cx);
+		if (!JS::Construct(rq.cx, protoval, JS::HandleValueArray(val), &obj))
 			throw PSERROR_Deserialize_ScriptError("JS_New failed");
 		AddScriptBackref(obj);
 		return JS::ObjectValue(*obj);
@@ -312,9 +314,10 @@
 		JS::RootedObject ctorobj(rq.cx);
 		if (!JS_GetClassObject(rq.cx, JSProto_Boolean, &ctorobj))
 			throw PSERROR_Deserialize_ScriptError("JS_GetClassObject failed");
+		JS::RootedValue protoval(rq.cx, JS::ObjectOrNullValue(ctorobj));
 
-		JS::RootedObject obj(rq.cx, JS_New(rq.cx, ctorobj, JS::HandleValueArray(val)));
-		if (!obj)
+		JS::RootedObject obj(rq.cx);
+		if (!JS::Construct(rq.cx, protoval, JS::HandleValueArray(val), &obj))
 			throw PSERROR_Deserialize_ScriptError("JS_New failed");
 		AddScriptBackref(obj);
 		return JS::ObjectValue(*obj);