1 files changed, 19 insertions, 0 deletions
diff --git a/js/src/tests/test262/built-ins/JSON/parse/duplicate-proto.js b/js/src/tests/test262/built-ins/JSON/parse/duplicate-proto.js
new file mode 100644
index 0000000000..93becbbc45
--- /dev/null
+++ b/js/src/tests/test262/built-ins/JSON/parse/duplicate-proto.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2020 devsnek. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-object-initializer-static-semantics-early-errors
+description: >
+  It is a Syntax Error if PropertyNameList of PropertyDefinitionList contains
+  any duplicate entries for "__proto__" and at least two of those entries were
+  obtained from productions of the form
+    PropertyDefinition : PropertyName `:` AssignmentExpression .
+  This rule is not applied if this PropertyDefinition is contained within a
+  Script which is being evaluated for JSON.parse (see step 4 of JSON.parse).
+---*/
+
+var result = JSON.parse('{ "__proto__": 1, "__proto__": 2 }');
+
+assert.sameValue(result.__proto__, 2);
+
+reportCompare(0, 0);