diff --git a/source/gui/GUIManager.cpp b/source/gui/GUIManager.cpp
index 4e22da8b6c..06bbe85231 100644
--- a/source/gui/GUIManager.cpp
+++ b/source/gui/GUIManager.cpp
@@ -261,11 +261,14 @@ Status CGUIManager::ReloadChangedFile(const VfsPath& path)
 
 CScriptVal CGUIManager::GetSavedGameData(ScriptInterface*& pPageScriptInterface)
 {
-	CScriptVal data;
-	if (!top()->GetScriptInterface()->CallFunction(top()->GetGlobalObject(), "getSavedGameData", data))
+	JSContext* cx = top()->GetScriptInterface()->GetContext();
+	JSAutoRequest rq(cx);
+	
+	JS::RootedValue data(cx);
+	if (!top()->GetScriptInterface()->CallFunction(top()->GetGlobalObject(), "getSavedGameData", &data))
 		LOGERROR(L"Failed to call getSavedGameData() on the current GUI page");
 	pPageScriptInterface = GetScriptInterface().get();
-	return data;
+	return CScriptVal(data);
 }
 
 std::string CGUIManager::GetSavedGameData()
diff --git a/source/scriptinterface/NativeWrapperDecls.h b/source/scriptinterface/NativeWrapperDecls.h
index a14c0afc33..54ea534d09 100644
--- a/source/scriptinterface/NativeWrapperDecls.h
+++ b/source/scriptinterface/NativeWrapperDecls.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2009 Wildfire Games.
+/* Copyright (C) 2014 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -26,6 +26,7 @@
 #define NUMBERED_LIST_BALANCED(z, i, data) BOOST_PP_COMMA_IF(i) data##i
 // Some other things
 #define TYPED_ARGS(z, i, data) , T##i a##i
+#define TYPED_ARGS_CONST_REF(z, i, data) const T##i& a##i,
 #define CONVERT_ARG(z, i, data) T##i a##i; if (! ScriptInterface::FromJSVal<T##i>(cx, i < args.length() ? args.handleAt(i) : JS::UndefinedHandleValue, a##i)) return false;
 
 // List-generating macros, named roughly after their first list item
@@ -35,6 +36,7 @@
 #define T0_HEAD(z, i) BOOST_PP_REPEAT_##z (i, NUMBERED_LIST_HEAD, T) // "T0, T1, "
 #define T0_TAIL(z, i) BOOST_PP_REPEAT_##z (i, NUMBERED_LIST_TAIL, T) // ", T0, T1"
 #define T0_A0(z, i) BOOST_PP_REPEAT_##z (i, TYPED_ARGS, ~) // "T0 a0, T1 a1"
+#define T0_A0_CONST_REF(z, i) BOOST_PP_REPEAT_##z (i, TYPED_ARGS_CONST_REF, ~) // " const T0 a0, const T1 a1, "
 #define A0(z, i) BOOST_PP_REPEAT_##z (i, NUMBERED_LIST_BALANCED, a) // "a0, a1"
 #define A0_TAIL(z, i) BOOST_PP_REPEAT_##z (i, NUMBERED_LIST_TAIL, a) // ", a0, a1"
 
@@ -68,3 +70,19 @@ BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
 	static size_t nargs() { return i; }
 BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
 #undef OVERLOADS
+
+// Call the named property on the given object
+#define OVERLOADS(z, i, data) \
+	template <typename R TYPENAME_T0_TAIL(z, i)> \
+	bool CallFunction(jsval val, const char* name, T0_A0_CONST_REF(z,i) R& ret);
+BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
+#undef OVERLOADS
+
+// The trick is using JS::Rooted<R>* and converting that to a JS::MutableHandle<R> explicitly in the function body.
+// Normally the function would take JS::MutableHandle<R> and that conversion would happen implicitly. However, implicit
+// conversion does not work with template argument deduction (only exact type matches allowed).
+#define OVERLOADS(z, i, data) \
+	template <typename R TYPENAME_T0_TAIL(z, i)> \
+	bool CallFunction(jsval val, const char* name, T0_A0_CONST_REF(z,i) JS::Rooted<R>* ret);
+BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
+#undef OVERLOADS
diff --git a/source/scriptinterface/NativeWrapperDefns.h b/source/scriptinterface/NativeWrapperDefns.h
index dc0aa37ebb..d84bd93ee3 100644
--- a/source/scriptinterface/NativeWrapperDefns.h
+++ b/source/scriptinterface/NativeWrapperDefns.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2009 Wildfire Games.
+/* Copyright (C) 2014 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -123,11 +123,52 @@ BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
 BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
 #undef OVERLOADS
 
+#define TO_JS_VAL(z, i, data) ToJSVal(cx, argv.handleAt(i), a##i);
+
+#define OVERLOADS(z, i, data) \
+template<typename R TYPENAME_T0_TAIL(z, i)> \
+bool ScriptInterface::CallFunction(jsval val, const char* name, T0_A0_CONST_REF(z,i) R& ret) \
+{ \
+	JSContext* cx = GetContext(); \
+	JSAutoRequest rq(cx); \
+	JS::RootedValue jsRet(cx); \
+	JS::RootedValue val1(cx, val); \
+	JS::AutoValueVector argv(cx); \
+	argv.resize(i); \
+	BOOST_PP_REPEAT_##z (i, TO_JS_VAL, ~) \
+	bool ok = CallFunction_(val1, name, argv.length(), argv.begin(), &jsRet); \
+	if (!ok) \
+		return false; \
+	return FromJSVal(cx, jsRet, ret); \
+}
+BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
+#undef OVERLOADS
+
+#define OVERLOADS(z, i, data) \
+template<typename R TYPENAME_T0_TAIL(z, i)> \
+bool ScriptInterface::CallFunction(jsval val, const char* name, T0_A0_CONST_REF(z,i) JS::Rooted<R>* ret) \
+{ \
+	JSContext* cx = GetContext(); \
+	JSAutoRequest rq(cx); \
+	JS::MutableHandle<R> jsRet(ret); \
+	JS::RootedValue val1(cx, val); \
+	JS::AutoValueVector argv(cx); \
+	argv.resize(i); \
+	BOOST_PP_REPEAT_##z (i, TO_JS_VAL, ~) \
+	bool ok = CallFunction_(val1, name, argv.length(), argv.begin(), jsRet); \
+	if (!ok) \
+		return false; \
+	return true; \
+}
+BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
+#undef OVERLOADS
+
 // Clean up our mess
 #undef SCRIPT_PROFILE
 #undef NUMBERED_LIST_HEAD
 #undef NUMBERED_LIST_TAIL
 #undef NUMBERED_LIST_BALANCED
+#undef TYPED_ARGS_CONST_REF
 #undef TYPED_ARGS
 #undef CONVERT_ARG
 #undef TYPENAME_T0_HEAD
@@ -135,6 +176,7 @@ BOOST_PP_REPEAT(SCRIPT_INTERFACE_MAX_ARGS, OVERLOADS, ~)
 #undef T0
 #undef T0_HEAD
 #undef T0_TAIL
+#undef T0_A0_CONST_REF
 #undef T0_A0
 #undef A0
 #undef A0_TAIL
diff --git a/source/scriptinterface/ScriptInterface.h b/source/scriptinterface/ScriptInterface.h
index b18e890c77..ff64d2f1d6 100644
--- a/source/scriptinterface/ScriptInterface.h
+++ b/source/scriptinterface/ScriptInterface.h
@@ -170,36 +170,6 @@ public:
 	template<typename T0, typename T1, typename T2>
 	bool CallFunctionVoid(jsval val, const char* name, const T0& a0, const T1& a1, const T2& a2);
 
-	/**
-	 * Call the named property on the given object, with return type R and 0 arguments
-	 */
-	template<typename R>
-	bool CallFunction(jsval val, const char* name, R& ret);
-
-	/**
-	 * Call the named property on the given object, with return type R and 1 argument
-	 */
-	template<typename T0, typename R>
-	bool CallFunction(jsval val, const char* name, const T0& a0, R& ret);
-
-	/**
-	 * Call the named property on the given object, with return type R and 2 arguments
-	 */
-	template<typename T0, typename T1, typename R>
-	bool CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, R& ret);
-
-	/**
-	 * Call the named property on the given object, with return type R and 3 arguments
-	 */
-	template<typename T0, typename T1, typename T2, typename R>
-	bool CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, const T2& a2, R& ret);
-
-	/**
-	 * Call the named property on the given object, with return type R and 4 arguments
-	 */
-	template<typename T0, typename T1, typename T2, typename T3, typename R>
-	bool CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, const T2& a2, const T3& a3, R& ret);
-
 	JSObject* CreateCustomObject(const std::string & typeName);
 	void DefineCustomObjectType(JSClass *clasp, JSNative constructor, uint minArgs, JSPropertySpec *ps, JSFunctionSpec *fs, JSPropertySpec *static_ps, JSFunctionSpec *static_fs);
 
@@ -444,19 +414,6 @@ public:
 // Implement those declared functions
 #include "NativeWrapperDefns.h"
 
-template<typename R>
-bool ScriptInterface::CallFunction(jsval val, const char* name, R& ret)
-{
-	JSContext* cx = GetContext();
-	JSAutoRequest rq(cx);
-	JS::RootedValue jsRet(cx);
-	JS::RootedValue val1(cx, val);
-	bool ok = CallFunction_(val1, name, 0, NULL, &jsRet);
-	if (!ok)
-		return false;
-	return FromJSVal(GetContext(), jsRet, ret);
-}
-
 template<typename T0>
 bool ScriptInterface::CallFunctionVoid(jsval val, const char* name, const T0& a0)
 {
@@ -499,76 +456,6 @@ bool ScriptInterface::CallFunctionVoid(jsval val, const char* name, const T0& a0
 	return CallFunction_(val1, name, 3, argv.begin(), &jsRet);
 }
 
-template<typename T0, typename R>
-bool ScriptInterface::CallFunction(jsval val, const char* name, const T0& a0, R& ret)
-{
-	JSContext* cx = GetContext();
-	JSAutoRequest rq(cx);
-	JS::RootedValue jsRet(cx);
-	JS::RootedValue val1(cx, val);
-	JS::AutoValueVector argv(cx);
-	argv.resize(1);
-	ToJSVal(cx, argv.handleAt(0), a0);
-	bool ok = CallFunction_(val1, name, 1, argv.begin(), &jsRet);
-	if (!ok)
-		return false;
-	return FromJSVal(cx, jsRet, ret);
-}
-
-template<typename T0, typename T1, typename R>
-bool ScriptInterface::CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, R& ret)
-{
-	JSContext* cx = GetContext();
-	JSAutoRequest rq(cx);
-	JS::RootedValue jsRet(cx);
-	JS::RootedValue val1(cx, val);
-	JS::AutoValueVector argv(cx);
-	argv.resize(2);
-	ToJSVal(cx, argv.handleAt(0), a0);
-	ToJSVal(cx, argv.handleAt(1), a1);
-	bool ok = CallFunction_(val1, name, 2, argv.begin(), &jsRet);
-	if (!ok)
-		return false;
-	return FromJSVal(cx, jsRet, ret);
-}
-
-template<typename T0, typename T1, typename T2, typename R>
-bool ScriptInterface::CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, const T2& a2, R& ret)
-{
-	JSContext* cx = GetContext();
-	JSAutoRequest rq(cx);
-	JS::RootedValue jsRet(cx);
-	JS::RootedValue val1(cx, val);
-	JS::AutoValueVector argv(cx);
-	argv.resize(3);
-	ToJSVal(cx, argv.handleAt(0), a0);
-	ToJSVal(cx, argv.handleAt(1), a1);
-	ToJSVal(cx, argv.handleAt(2), a2);
-	bool ok = CallFunction_(val1, name, 3, argv.begin(), &jsRet);
-	if (!ok)
-		return false;
-	return FromJSVal(cx, jsRet, ret);
-}
-
-template<typename T0, typename T1, typename T2, typename T3, typename R>
-bool ScriptInterface::CallFunction(jsval val, const char* name, const T0& a0, const T1& a1, const T2& a2, const T3& a3, R& ret)
-{
-	JSContext* cx = GetContext();
-	JSAutoRequest rq(cx);
-	JS::RootedValue jsRet(cx);
-	JS::RootedValue val1(cx, val);
-	JS::AutoValueVector argv(cx);
-	argv.resize(4);
-	ToJSVal(cx, argv.handleAt(0), a0);
-	ToJSVal(cx, argv.handleAt(1), a1);
-	ToJSVal(cx, argv.handleAt(2), a2);
-	ToJSVal(cx, argv.handleAt(3), a3);
-	bool ok = CallFunction_(val1, name, 4, argv.begin(), &jsRet);
-	if (!ok)
-		return false;
-	return FromJSVal(cx, jsRet, ret);
-}
-
 template<typename T>
 bool ScriptInterface::SetGlobal(const char* name, const T& value, bool replace)
 {