diff --git a/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-false-for-zero.js b/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-false-for-zero.js
new file mode 100644
index 0000000000..286a0e4e36
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-false-for-zero.js
@@ -0,0 +1,46 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.includes
+description: Returns -1 if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.includes are the same as for Array.prototype.includes as defined in 22.1.3.13.
+
+  When the includes method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return false.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return false.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+    If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let elementK be the result of ! Get(O, ! ToString(F(k))).
+    If SameValueZero(searchElement, elementK) is true, return true.
+    Set k to k + 1.
+  Return false.
+
+includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, BigInt, TypedArray]
+---*/
+
+testWithBigIntTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.includes(0n, fromIndex), false);
+});
diff --git a/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-true-for-undefined.js b/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-true-for-undefined.js
new file mode 100644
index 0000000000..329985324f
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/includes/BigInt/detached-buffer-during-fromIndex-returns-true-for-undefined.js
@@ -0,0 +1,47 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.includes
+description: >
+  Returns false if buffer is detached after ValidateTypedArray and searchElement is a value
+info: |
+  %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.includes are the same as for Array.prototype.includes as defined in 22.1.3.13.
+
+  When the includes method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return false.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return false.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+    If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let elementK be the result of ! Get(O, ! ToString(F(k))).
+    If SameValueZero(searchElement, elementK) is true, return true.
+    Set k to k + 1.
+  Return false.
+
+includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, BigInt, TypedArray]
+---*/
+
+testWithBigIntTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.includes(undefined, fromIndex), true);
+});
diff --git a/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-false-for-zero.js b/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-false-for-zero.js
new file mode 100644
index 0000000000..6ac449e9a1
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-false-for-zero.js
@@ -0,0 +1,47 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.includes
+description: >
+  Returns false if buffer is detached after ValidateTypedArray and searchElement is a value
+info: |
+  %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.includes are the same as for Array.prototype.includes as defined in 22.1.3.13.
+
+  When the includes method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return false.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return false.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+    If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let elementK be the result of ! Get(O, ! ToString(F(k))).
+    If SameValueZero(searchElement, elementK) is true, return true.
+    Set k to k + 1.
+  Return false.
+
+includes: [testTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
+---*/
+
+testWithTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.includes(0, fromIndex), false);
+});
diff --git a/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-true-for-undefined.js b/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-true-for-undefined.js
new file mode 100644
index 0000000000..e524e28759
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/includes/detached-buffer-during-fromIndex-returns-true-for-undefined.js
@@ -0,0 +1,47 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.includes
+description: >
+  Returns true if buffer is detached after ValidateTypedArray and searchElement is undefined
+info: |
+  %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.includes are the same as for Array.prototype.includes as defined in 22.1.3.13.
+
+  When the includes method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return false.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return false.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+    If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let elementK be the result of ! Get(O, ! ToString(F(k))).
+    If SameValueZero(searchElement, elementK) is true, return true.
+    Set k to k + 1.
+  Return false.
+
+includes: [testTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
+---*/
+
+testWithTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.includes(undefined, fromIndex), true);
+});
diff --git a/test/built-ins/TypedArray/prototype/includes/detached-buffer-tointeger.js b/test/built-ins/TypedArray/prototype/includes/detached-buffer-tointeger.js
deleted file mode 100644
index 9eebb34c2e..0000000000
--- a/test/built-ins/TypedArray/prototype/includes/detached-buffer-tointeger.js
+++ /dev/null
@@ -1,37 +0,0 @@
-// Copyright (C) 2020 Google. All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-/*---
-esid: sec-%typedarray%.prototype.includes
-description: >
-  Does not throw a TypeError if this has a detached buffer after index coercion,
-  because ValidateTypedArray has already successfully completed.
-
-info: |
-  22.2.3.14 %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
-
-  The interpretation and use of the arguments of %TypedArray%.prototype.includes are the same as for Array.prototype.includes as defined in 22.1.3.13.
-
-  When the includes method is called with one or two arguments, the following steps are taken:
-
-  Let O be the this value.
-  Perform ? ValidateTypedArray(O).
-  Let len be O.[[ArrayLength]].
-  If len is 0, return false.
-  Let n be ? ToIntegerOrInfinity(fromIndex).
-  ...
-
-includes: [testTypedArray.js, detachArrayBuffer.js]
-features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
----*/
-
-testWithTypedArrayConstructors(function(TA) {
-  const sample = new TA(10);
-  let isDetached = false;
-  function valueOf(){
-    $DETACHBUFFER(sample.buffer);
-    isDetached = true;
-    return 0;
-  }
-  assert.sameValue(sample.includes(0, {valueOf}), false);
-  assert.sameValue(isDetached, true);
-});
diff --git a/test/built-ins/TypedArray/prototype/indexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js b/test/built-ins/TypedArray/prototype/indexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js
new file mode 100644
index 0000000000..b357ad216b
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/indexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js
@@ -0,0 +1,49 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.indexof
+description: Throws a TypeError if this has a detached buffer
+info: |
+  %TypedArray%.prototype.indexOf ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.indexOf are the same as for Array.prototype.indexOf as defined in 22.1.3.14.
+
+  When the indexOf method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return -1F.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return -1F.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+  If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let kPresent be ! HasProperty(O, ! ToString(F(k))).
+    If kPresent is true, then
+      Let elementK be ! Get(O, ! ToString(F(k))).
+      Let same be the result of performing Strict Equality Comparison searchElement === elementK.
+      If same is true, return F(k).
+    Set k to k + 1.
+  Return -1F.
+
+includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, BigInt, TypedArray]
+---*/
+
+testWithBigIntTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.indexOf(0n, fromIndex), -1);
+});
diff --git a/test/built-ins/TypedArray/prototype/indexOf/detached-buffer-during-fromIndex-returns-minus-one.js b/test/built-ins/TypedArray/prototype/indexOf/detached-buffer-during-fromIndex-returns-minus-one.js
new file mode 100644
index 0000000000..4dc25bf11b
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/indexOf/detached-buffer-during-fromIndex-returns-minus-one.js
@@ -0,0 +1,49 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.indexof
+description: Returns -1 if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.indexOf ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.indexOf are the same as for Array.prototype.indexOf as defined in 22.1.3.14.
+
+  When the indexOf method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return -1F.
+  Let n be ? ToIntegerOrInfinity(fromIndex).
+  Assert: If fromIndex is undefined, then n is 0.
+  If n is +∞, return -1F.
+  Else if n is -∞, set n to 0.
+  If n ≥ 0, then
+    Let k be n.
+  Else,
+    Let k be len + n.
+  If k < 0, set k to 0.
+  Repeat, while k < len,
+    Let kPresent be ! HasProperty(O, ! ToString(F(k))).
+    If kPresent is true, then
+      Let elementK be ! Get(O, ! ToString(F(k))).
+      Let same be the result of performing Strict Equality Comparison searchElement === elementK.
+      If same is true, return F(k).
+    Set k to k + 1.
+  Return -1F.
+
+includes: [testTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
+---*/
+
+testWithTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.indexOf(0, fromIndex), -1);
+});
diff --git a/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer-during-fromIndex-returns-single-comma.js b/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer-during-fromIndex-returns-single-comma.js
new file mode 100644
index 0000000000..7b1e6e67a1
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer-during-fromIndex-returns-single-comma.js
@@ -0,0 +1,42 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.join
+description: Returns single separator if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.join ( separator )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.join are the same as for Array.prototype.join as defined in 22.1.3.15.
+
+  When the join method is called with one argument separator, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If separator is undefined, let sep be the single-element String ",".
+  Else, let sep be ? ToString(separator).
+  Let R be the empty String.
+  Let k be 0.
+  Repeat, while k < len,
+    If k > 0, set R to the string-concatenation of R and sep.
+    Let element be ! Get(O, ! ToString(𝔽(k))).
+    If element is undefined or null, let next be the empty String; otherwise, let next be ! ToString(element).
+    Set R to the string-concatenation of R and next.
+    Set k to k + 1.
+  Return R.
+
+includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, BigInt, TypedArray]
+---*/
+
+testWithBigIntTypedArrayConstructors(function(TA) {
+  const sample = new TA([1n,2n,3n]);
+  const separator = {
+    toString() {
+      $DETACHBUFFER(sample.buffer);
+      return ',';
+    }
+  };
+
+  assert.sameValue(sample.join(separator), ',,');
+});
diff --git a/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer.js b/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer.js
index 1af7ae94c5..e4c91a5409 100644
--- a/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer.js
+++ b/test/built-ins/TypedArray/prototype/join/BigInt/detached-buffer.js
@@ -4,31 +4,30 @@
 esid: sec-%typedarray%.prototype.join
 description: Throws a TypeError if this has a detached buffer
 info: |
-  22.2.3.15 %TypedArray%.prototype.join ( separator )
+  %TypedArray%.prototype.join ( separator )
 
-  This function is not generic. ValidateTypedArray is applied to the this value
-  prior to evaluating the algorithm. If its result is an abrupt completion that
-  exception is thrown instead of evaluating the algorithm.
+  The interpretation and use of the arguments of %TypedArray%.prototype.join are the same as for Array.prototype.join as defined in 22.1.3.15.
 
-  22.2.3.5.1 Runtime Semantics: ValidateTypedArray ( O )
+  When the join method is called with one argument separator, the following steps are taken:
 
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
   ...
-  5. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
-  ...
+
 includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
 features: [BigInt, TypedArray]
 ---*/
 
-var obj = {
-  toString: function() {
+let obj = {
+  toString() {
     throw new Test262Error();
   }
 };
 
 testWithBigIntTypedArrayConstructors(function(TA) {
-  var sample = new TA(1);
+  let sample = new TA(1);
   $DETACHBUFFER(sample.buffer);
-  assert.throws(TypeError, function() {
+  assert.throws(TypeError, () => {
     sample.join(obj);
   });
 });
diff --git a/test/built-ins/TypedArray/prototype/join/detached-buffer-during-fromIndex-returns-single-comma.js b/test/built-ins/TypedArray/prototype/join/detached-buffer-during-fromIndex-returns-single-comma.js
new file mode 100644
index 0000000000..e1edd3a519
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/join/detached-buffer-during-fromIndex-returns-single-comma.js
@@ -0,0 +1,42 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.join
+description: Returns single separator if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.join ( separator )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.join are the same as for Array.prototype.join as defined in 22.1.3.15.
+
+  When the join method is called with one argument separator, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If separator is undefined, let sep be the single-element String ",".
+  Else, let sep be ? ToString(separator).
+  Let R be the empty String.
+  Let k be 0.
+  Repeat, while k < len,
+    If k > 0, set R to the string-concatenation of R and sep.
+    Let element be ! Get(O, ! ToString(𝔽(k))).
+    If element is undefined or null, let next be the empty String; otherwise, let next be ! ToString(element).
+    Set R to the string-concatenation of R and next.
+    Set k to k + 1.
+  Return R.
+
+includes: [testTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
+---*/
+
+testWithTypedArrayConstructors(function(TA) {
+  const sample = new TA([1,2,3]);
+  const separator = {
+    toString() {
+      $DETACHBUFFER(sample.buffer);
+      return ',';
+    }
+  };
+
+  assert.sameValue(sample.join(separator), ',,');
+});
diff --git a/test/built-ins/TypedArray/prototype/join/detached-buffer.js b/test/built-ins/TypedArray/prototype/join/detached-buffer.js
index b737c9f91a..0d78c2b091 100644
--- a/test/built-ins/TypedArray/prototype/join/detached-buffer.js
+++ b/test/built-ins/TypedArray/prototype/join/detached-buffer.js
@@ -4,31 +4,30 @@
 esid: sec-%typedarray%.prototype.join
 description: Throws a TypeError if this has a detached buffer
 info: |
-  22.2.3.15 %TypedArray%.prototype.join ( separator )
+  %TypedArray%.prototype.join ( separator )
 
-  This function is not generic. ValidateTypedArray is applied to the this value
-  prior to evaluating the algorithm. If its result is an abrupt completion that
-  exception is thrown instead of evaluating the algorithm.
+  The interpretation and use of the arguments of %TypedArray%.prototype.join are the same as for Array.prototype.join as defined in 22.1.3.15.
 
-  22.2.3.5.1 Runtime Semantics: ValidateTypedArray ( O )
+  When the join method is called with one argument separator, the following steps are taken:
 
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
   ...
-  5. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
-  ...
+
 includes: [testTypedArray.js, detachArrayBuffer.js]
 features: [TypedArray]
 ---*/
 
-var obj = {
-  toString: function() {
+let obj = {
+  toString() {
     throw new Test262Error();
   }
 };
 
 testWithTypedArrayConstructors(function(TA) {
-  var sample = new TA(1);
+  let sample = new TA(1);
   $DETACHBUFFER(sample.buffer);
-  assert.throws(TypeError, function() {
+  assert.throws(TypeError, () => {
     sample.join(obj);
   });
 });
diff --git a/test/built-ins/TypedArray/prototype/lastIndexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js b/test/built-ins/TypedArray/prototype/lastIndexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js
new file mode 100644
index 0000000000..16fef1d6ae
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/lastIndexOf/BigInt/detached-buffer-during-fromIndex-returns-minus-one.js
@@ -0,0 +1,46 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.lastindexof
+description: Returns -1 if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.lastIndexOf are the same as for Array.prototype.lastIndexOf as defined in 22.1.3.17.
+
+  When the lastIndexOf method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return -1F.
+  If fromIndex is present, let n be ? ToIntegerOrInfinity(fromIndex); else let n be len - 1.
+  If n is -∞, return -1F.
+  If n ≥ 0, then
+    Let k be min(n, len - 1).
+  Else,
+    Let k be len + n.
+  Repeat, while k ≥ 0,
+    Let kPresent be ! HasProperty(O, ! ToString(F(k))).
+    If kPresent is true, then
+      Let elementK be ! Get(O, ! ToString(F(k))).
+      Let same be the result of performing Strict Equality Comparison searchElement === elementK.
+      If same is true, return F(k).
+    Set k to k - 1.
+  Return -1F.
+
+includes: [testBigIntTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, BigInt, TypedArray]
+---*/
+
+testWithBigIntTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.lastIndexOf(0n, fromIndex), -1);
+});
diff --git a/test/built-ins/TypedArray/prototype/lastIndexOf/detached-buffer-during-fromIndex-returns-minus-one.js b/test/built-ins/TypedArray/prototype/lastIndexOf/detached-buffer-during-fromIndex-returns-minus-one.js
new file mode 100644
index 0000000000..90096ada09
--- /dev/null
+++ b/test/built-ins/TypedArray/prototype/lastIndexOf/detached-buffer-during-fromIndex-returns-minus-one.js
@@ -0,0 +1,46 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.lastindexof
+description: Returns -1 if buffer is detached after ValidateTypedArray
+info: |
+  %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
+
+  The interpretation and use of the arguments of %TypedArray%.prototype.lastIndexOf are the same as for Array.prototype.lastIndexOf as defined in 22.1.3.17.
+
+  When the lastIndexOf method is called with one or two arguments, the following steps are taken:
+
+  Let O be the this value.
+  Perform ? ValidateTypedArray(O).
+  Let len be O.[[ArrayLength]].
+  If len is 0, return -1F.
+  If fromIndex is present, let n be ? ToIntegerOrInfinity(fromIndex); else let n be len - 1.
+  If n is -∞, return -1F.
+  If n ≥ 0, then
+    Let k be min(n, len - 1).
+  Else,
+    Let k be len + n.
+  Repeat, while k ≥ 0,
+    Let kPresent be ! HasProperty(O, ! ToString(F(k))).
+    If kPresent is true, then
+      Let elementK be ! Get(O, ! ToString(F(k))).
+      Let same be the result of performing Strict Equality Comparison searchElement === elementK.
+      If same is true, return F(k).
+    Set k to k - 1.
+  Return -1F.
+
+includes: [testTypedArray.js, detachArrayBuffer.js]
+features: [align-detached-buffer-semantics-with-web-reality, TypedArray]
+---*/
+
+testWithTypedArrayConstructors(function(TA) {
+  const sample = new TA(1);
+  const fromIndex = {
+    valueOf() {
+      $DETACHBUFFER(sample.buffer);
+      return 0;
+    }
+  };
+
+  assert.sameValue(sample.lastIndexOf(0, fromIndex), -1);
+});
diff --git a/test/built-ins/TypedArrayConstructors/internals/Set/detached-buffer.js b/test/built-ins/TypedArrayConstructors/internals/Set/detached-buffer.js
index c708844a40..6c2ce33e12 100644
--- a/test/built-ins/TypedArrayConstructors/internals/Set/detached-buffer.js
+++ b/test/built-ins/TypedArrayConstructors/internals/Set/detached-buffer.js
@@ -30,6 +30,7 @@ testWithTypedArrayConstructors(function(TA) {
   let sample = new TA([42]);
   $DETACHBUFFER(sample.buffer);
   sample[0] = 1;
+
   assert.sameValue(sample[0], undefined, '`sample[0] = 1` is undefined');
   sample['1.1'] = 1;
   assert.sameValue(sample['1.1'], undefined, '`sample[\'1.1\'] = 1` is undefined');