Index: source/scriptinterface/ScriptConversions.cpp
===================================================================
--- source/scriptinterface/ScriptConversions.cpp
+++ source/scriptinterface/ScriptConversions.cpp
@@ -158,16 +158,10 @@
 
 template<> bool ScriptInterface::FromJSVal<std::string>(JSContext* cx, JS::HandleValue v, std::string& out)
 {
-	JSAutoRequest rq(cx);
-	WARN_IF_NOT(v.isString() || v.isNumber(), v); // allow implicit number conversions
-	JS::RootedString str(cx, JS::ToString(cx, v));
-	if (!str)
-		FAIL("Argument must be convertible to a string");
-	char* ch = JS_EncodeString(cx, str); // chops off high byte of each char16_t
-	if (!ch)
-		FAIL("JS_EncodeString failed"); // out of memory
-	out.assign(ch, ch + JS_GetStringLength(str));
-	JS_free(cx, ch);
+	std::wstring wideout;
+	if (!FromJSVal(cx, v, wideout))
+		return false;
+	out = CStrW(wideout).ToUTF8();
 	return true;
 }
 
@@ -265,12 +259,7 @@
 
 template<> void ScriptInterface::ToJSVal<std::string>(JSContext* cx, JS::MutableHandleValue ret, const std::string& val)
 {
-	JSAutoRequest rq(cx);
-	JS::RootedString str(cx, JS_NewStringCopyN(cx, val.c_str(), val.length()));
-	if (str)
-		ret.setString(str);
-	else
-		ret.setUndefined();
+	ToJSVal(cx, ret, static_cast<const std::wstring>(CStr(val).FromUTF8()));
 }
 
 template<> void ScriptInterface::ToJSVal<const wchar_t*>(JSContext* cx, JS::MutableHandleValue ret, const wchar_t* const& val)
Index: source/scriptinterface/tests/test_ScriptConversions.h
===================================================================
--- source/scriptinterface/tests/test_ScriptConversions.h
+++ source/scriptinterface/tests/test_ScriptConversions.h
@@ -51,7 +51,7 @@
 	}
 
 	template <typename T>
-	void roundtrip(const T& value, const char* expected)
+	T roundtrip(const T& value, const char* expected)
 	{
 		ScriptInterface script("Test", "Test", g_ScriptRuntime);
 		TS_ASSERT(script.LoadGlobalScripts());
@@ -71,6 +71,7 @@
 		T v2 = T();
 		TS_ASSERT(ScriptInterface::FromJSVal(cx, v1, v2));
 		TS_ASSERT_EQUALS(value, v2);
+		return v2;
 	}
 
 	template <typename T>
@@ -148,9 +149,9 @@
 
 		roundtrip<std::string>("", "\"\"");
 		roundtrip<std::string>("test", "\"test\"");
-		roundtrip<std::string>("тест", "\"\\xD1\\x82\\xD0\\xB5\\xD1\\x81\\xD1\\x82\"");
+		TS_ASSERT_EQUALS(roundtrip<std::string>("тест", "\"\\u0442\\u0435\\u0441\\u0442\""), "тест");
 		roundtrip<std::string>(s1, "\"t\\x00st\"");
-		roundtrip<std::string>(s2, "\"\\xD1\\x82\\x00\\x00\\xD1\\x81\\xD1\\x82\"");
+		TS_ASSERT_EQUALS(roundtrip<std::string>(s2, "\"\\u0442\\x00\\x00\\u0441\\u0442\""), s2);
 
 		roundtrip<std::wstring>(L"", "\"\"");
 		roundtrip<std::wstring>(L"test", "\"test\"");
@@ -251,4 +252,37 @@
 		CFixedVector3D u(fixed::Pi(), fixed::Zero(), fixed::FromInt(2));
 		call_prototype_function<CFixedVector3D>(u, v, "add", "({x:3.1415863037109375, y:3.1415863037109375, z:3})");
 	}
+
+	void test_strings()
+	{
+		{
+			std::string test("éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+			TS_ASSERT_EQUALS(test, roundtrip<std::string>(test, nullptr));
+		}
+		{
+			std::wstring test(L"éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+			TS_ASSERT_EQUALS(test, roundtrip<std::wstring>(test, nullptr));
+		}
+		ScriptInterface script("Test", "Test", g_ScriptRuntime);
+		TS_ASSERT(script.LoadGlobalScripts());
+		JSContext* cx = script.GetContext();
+		JSAutoRequest rq(cx);
+		{
+			// Fancier conversion: we store UTF8 and get UTF16 and vice-versa
+			std::string in_utf8("éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+			std::wstring in_utf16(L"éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+
+			JS::RootedValue v1(cx);
+			ScriptInterface::ToJSVal(cx, &v1, in_utf8);
+
+			std::wstring test_out_utf16;
+			TS_ASSERT(ScriptInterface::FromJSVal(cx, v1, test_out_utf16));
+			TS_ASSERT_EQUALS(test_out_utf16, in_utf16);
+			// Start clean.
+			ScriptInterface::ToJSVal(cx, &v1, in_utf16);
+			std::string test_out_utf8;
+			TS_ASSERT(ScriptInterface::FromJSVal(cx, v1, test_out_utf8));
+			TS_ASSERT_EQUALS(test_out_utf8, in_utf8);
+		}
+	}
 };