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diff --git a/js/src/tests/test262/built-ins/Proxy/getPrototypeOf/instanceof-target-not-extensible-not-same-proto-throws.js b/js/src/tests/test262/built-ins/Proxy/getPrototypeOf/instanceof-target-not-extensible-not-same-proto-throws.js
new file mode 100644
index 0000000000..7084f5e92a
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+++ b/js/src/tests/test262/built-ins/Proxy/getPrototypeOf/instanceof-target-not-extensible-not-same-proto-throws.js
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+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-proxy-object-internal-methods-and-internal-slots-getprototypeof
+description: >
+  instanceof operator observes the TypeError from a custom trap result that would return true if
+  the target were extensible.
+info: |
+  Runtime Semantics: InstanceofOperator ( V, target )
+
+  5. Return ? OrdinaryHasInstance(target, V).
+
+  OrdinaryHasInstance ( C, O )
+
+  4. Let P be ? Get(C, "prototype").
+  ...
+  6. Repeat,
+    a. Set O to ? O.[[GetPrototypeOf]]().
+    b. If O is null, return false.
+    c. If SameValue(P, O) is true, return true.
+
+  [[GetPrototypeOf]] ( )
+
+  7. Let handlerProto be ? Call(trap, handler, « target »).
+  8. If Type(handlerProto) is neither Object nor Null, throw a TypeError exception.
+  9. Let extensibleTarget be ? IsExtensible(target).
+  10. If extensibleTarget is true, return handlerProto.
+  11. Let targetProto be ? target.[[GetPrototypeOf]]().
+  12. If SameValue(handlerProto, targetProto) is false, throw a TypeError exception.
+features: [Proxy]
+---*/
+
+function Custom() {}
+
+var target = {};
+
+var p = new Proxy(target, {
+  getPrototypeOf() {
+    return Custom.prototype;
+  }
+});
+
+Object.preventExtensions(target);
+
+assert.throws(TypeError, () => {
+  p instanceof Custom
+});
+
+reportCompare(0, 0);