diff --git a/src/builtins/array-reverse.tq b/src/builtins/array-reverse.tq
index 7cfef719db..8db542ddef 100644
--- a/src/builtins/array-reverse.tq
+++ b/src/builtins/array-reverse.tq
@@ -143,14 +143,25 @@ module array {
     return object;
   }
 
+  macro EnsureWriteableFastElements(array: JSArray) {
+    const elements: FixedArrayBase = array.elements;
+    if (elements.map != kCOWMap) return;
+
+    // There are no COW *_DOUBLE_ELEMENTS arrays, so we are allowed to always
+    // extract FixedArrays and don't have to worry about FixedDoubleArrays.
+    assert(IsFastSmiOrTaggedElementsKind(array.map.elements_kind));
+
+    const length: Smi = array.length_fast;
+    array.elements = ExtractFixedArray(
+        unsafe_cast<FixedArray>(elements), 0, length, length, kFixedArrays);
+  }
+
   macro TryFastPackedArrayReverse(receiver: Object) labels Slow {
     const array: JSArray = cast<JSArray>(receiver) otherwise Slow;
-    const map: Map = array.map;
+    EnsureWriteableFastElements(array);
+    assert(array.elements.map != kCOWMap);
 
-    if (!IsExtensibleMap(map)) goto Slow;
-    if (array.elements.map == kCOWMap) goto Slow;
-
-    const kind: ElementsKind = map.elements_kind;
+    const kind: ElementsKind = array.map.elements_kind;
     if (kind == PACKED_SMI_ELEMENTS) {
       FastPackedArrayReverse<FastPackedSmiElements, Smi>(
           array.elements, array.length_fast);
diff --git a/src/builtins/base.tq b/src/builtins/base.tq
index 0707632b0b..1b9d577f10 100644
--- a/src/builtins/base.tq
+++ b/src/builtins/base.tq
@@ -109,6 +109,8 @@ type FixedBigInt64Array extends FixedTypedArray;
 
 const kAllFixedArrays: constexpr ExtractFixedArrayFlags generates
 'ExtractFixedArrayFlag::kAllFixedArrays';
+const kFixedArrays: constexpr ExtractFixedArrayFlags generates
+'ExtractFixedArrayFlag::kFixedArrays';
 
 const kFixedCOWArrayMapRootIndex: constexpr RootListIndex generates
 'Heap::kFixedCOWArrayMapRootIndex';