diff --git a/compiler_test.go b/compiler_test.go
index bbacbf4a..22215f2e 100644
--- a/compiler_test.go
+++ b/compiler_test.go
@@ -4113,6 +4113,17 @@ func TestArrowUseStrict(t *testing.T) {
 	}
 }
 
+func TestParameterOverride(t *testing.T) {
+	const SCRIPT = `
+	function f(arg) {
+		var arg = arg || "default"
+		return arg
+	}
+	f()
+	`
+	testScript1(SCRIPT, asciiString("default"), t)
+}
+
 /*
 func TestBabel(t *testing.T) {
 	src, err := ioutil.ReadFile("babel7.js")
diff --git a/vm.go b/vm.go
index 43b6799d..fb95a81c 100644
--- a/vm.go
+++ b/vm.go
@@ -2326,7 +2326,7 @@ func (r *resolveMixedStack) exec(vm *vm) {
 	if r.idx > 0 {
 		idx = vm.sb + vm.args + r.idx
 	} else {
-		idx = vm.sb + r.idx
+		idx = vm.sb - r.idx
 	}
 
 	ref = newStashRef(r.typ, r.name, (*[]Value)(&vm.stack), idx)