diff --git a/scripts/build/deps/webkit.ts b/scripts/build/deps/webkit.ts
index 7e8ddecce2ac..c643c6824de6 100644
--- a/scripts/build/deps/webkit.ts
+++ b/scripts/build/deps/webkit.ts
@@ -3,7 +3,7 @@
  * for local mode. Override via `--webkit-version=<hash>` to test a branch.
  * From https://github.com/oven-sh/WebKit releases.
  */
-export const WEBKIT_VERSION = "2e2aa2290fac856d6f451ceacb58f7f5b44dd057";
+export const WEBKIT_VERSION = "autobuild-preview-pr-607-bb622e7b";
 
 /**
  * WebKit (JavaScriptCore) — the JS engine.
diff --git a/test/js/bun/jsc/bigint-typed-array-index-of.test.ts b/test/js/bun/jsc/bigint-typed-array-index-of.test.ts
new file mode 100644
index 000000000000..a604dbe00373
--- /dev/null
+++ b/test/js/bun/jsc/bigint-typed-array-index-of.test.ts
@@ -0,0 +1,164 @@
+import { describe, expect, test } from "bun:test";
+
+// BigInt64Array / BigUint64Array .indexOf, .lastIndexOf and .includes compare
+// the needle with each element's BigInt value (IsStrictlyEqual /
+// SameValueZero). A BigInt the element type cannot represent never matches.
+// JSC used to convert the needle with a wrapping ToBigInt64 / ToBigUint64, so
+// a needle congruent to an element modulo 2^64 was reported as found:
+// `new BigInt64Array([-1n]).includes(2n ** 64n - 1n)` was true.
+
+const int64Max = 2n ** 63n - 1n;
+const int64Min = -(2n ** 63n);
+const uint64Max = 2n ** 64n - 1n;
+
+type Case = [elements: bigint[], needle: bigint, expectedIndex: number];
+
+const int64Cases: Case[] = [
+  [[3n, -1n, 7n], 2n ** 64n - 1n, -1], // wraps to -1n
+  [[3n, -1n, 7n], 2n ** 64n + 3n, -1], // wraps to 3n
+  [[3n, -1n, 7n], -(2n ** 64n) + 7n, -1], // wraps to 7n
+  [[3n, 0n, 7n], 2n ** 64n, -1], // wraps to 0n
+  [[3n, 0n, 7n], -(2n ** 64n), -1], // wraps to 0n
+  [[3n, 0n, 7n], 2n ** 128n, -1], // wraps to 0n
+  [[3n, int64Min, 7n], 2n ** 63n, -1], // wraps to -2^63
+  [[3n, int64Max, 7n], int64Min - 1n, -1], // wraps to 2^63 - 1
+  [[3n, 5n, 7n], 2n ** 200n + 5n, -1], // many digits, low 64 bits are 5
+  [[3n, -5n, 7n], -(2n ** 200n) - 5n, -1],
+  // Representable needles still match, including the boundaries.
+  [[3n, -1n, 7n], -1n, 1],
+  [[3n, -1n, 7n], 3n, 0],
+  [[3n, -1n, 7n], 7n, 2],
+  [[3n, 0n, 7n], 0n, 1],
+  [[3n, int64Max, 7n], int64Max, 1],
+  [[3n, int64Min, 7n], int64Min, 1],
+  [[3n, 2n ** 32n, 7n], 2n ** 32n, 1],
+  [[3n, -(2n ** 32n), 7n], -(2n ** 32n), 1],
+  [[3n, -1n, 7n], 4n, -1],
+];
+
+const uint64Cases: Case[] = [
+  [[3n, uint64Max, 7n], -1n, -1], // wraps to 2^64 - 1
+  [[3n, int64Max, 7n], int64Min - 1n, -1], // wraps to 2^63 - 1
+  [[3n, 2n ** 63n, 7n], int64Min, -1], // wraps to 2^63
+  [[3n, 0n, 7n], 2n ** 64n, -1], // wraps to 0n
+  [[3n, 0n, 7n], -(2n ** 64n), -1], // wraps to 0n
+  [[3n, 0n, 7n], 2n ** 128n, -1], // wraps to 0n
+  [[3n, 5n, 7n], 2n ** 64n + 5n, -1], // wraps to 5n
+  [[3n, 5n, 7n], -(2n ** 64n) + 5n, -1], // wraps to 5n
+  [[3n, 5n, 7n], 2n ** 200n + 5n, -1],
+  [[3n, uint64Max - 4n, 7n], -5n, -1], // wraps to 2^64 - 5
+  // Representable needles still match, including the boundaries.
+  [[3n, uint64Max, 7n], uint64Max, 1],
+  [[3n, 0n, 7n], 0n, 1],
+  [[3n, 2n ** 63n, 7n], 2n ** 63n, 1],
+  [[3n, int64Max, 7n], int64Max, 1],
+  [[3n, 2n ** 32n, 7n], 2n ** 32n, 1],
+  [[3n, 5n, 7n], 3n, 0],
+  [[3n, 5n, 7n], 7n, 2],
+  [[3n, 5n, 7n], 4n, -1],
+];
+
+type BigIntArrayConstructor = BigInt64ArrayConstructor | BigUint64ArrayConstructor;
+
+// The same elements seen through a plain view, a subarray, a length-tracking
+// view of a resizable buffer, a fixed window of one, and a shared buffer.
+function makeViews(constructor: BigIntArrayConstructor, elements: bigint[]) {
+  const byteLength = elements.length * 8;
+
+  const plain = new constructor(elements);
+
+  const padded = new constructor(elements.length + 2);
+  padded.set(elements, 1);
+  const subarray = padded.subarray(1, elements.length + 1);
+
+  const resizable = new ArrayBuffer(byteLength, { maxByteLength: byteLength + 64 });
+  const tracking = new constructor(resizable);
+  tracking.set(elements);
+  const fixedWindow = new constructor(resizable, 0, elements.length);
+
+  const shared = new constructor(new SharedArrayBuffer(byteLength));
+  shared.set(elements);
+
+  return { plain, subarray, tracking, fixedWindow, shared };
+}
+
+function search(array: BigInt64Array | BigUint64Array, needle: bigint) {
+  return {
+    indexOf: array.indexOf(needle),
+    lastIndexOf: array.lastIndexOf(needle),
+    includes: array.includes(needle),
+    indexOfFrom1: array.indexOf(needle, 1),
+    lastIndexOfFromMinus2: array.lastIndexOf(needle, -2),
+    includesFromMinus1: array.includes(needle, -1),
+    // The generic Array.prototype path was always correct. It is the reference.
+    arrayIndexOf: Array.prototype.indexOf.call(array, needle),
+    arrayIncludes: Array.prototype.includes.call(array, needle),
+  };
+}
+
+function expected(length: number, index: number) {
+  return {
+    indexOf: index,
+    lastIndexOf: index,
+    includes: index !== -1,
+    indexOfFrom1: index >= 1 ? index : -1,
+    lastIndexOfFromMinus2: index <= length - 2 ? index : -1,
+    includesFromMinus1: index === length - 1,
+    arrayIndexOf: index,
+    arrayIncludes: index !== -1,
+  };
+}
+
+describe.each([
+  ["BigInt64Array", BigInt64Array, int64Cases],
+  ["BigUint64Array", BigUint64Array, uint64Cases],
+] as const)("%s indexOf / lastIndexOf / includes", (_name, constructor, cases) => {
+  test.each(
+    cases.map(
+      ([elements, needle, index]) => [`${needle}n`, `[${elements.join("n, ")}n]`, elements, needle, index] as const,
+    ),
+  )("needle %s in %s", (_needle, _elements, elements, needle, index) => {
+    for (const [kind, view] of Object.entries(makeViews(constructor, elements))) {
+      expect({ kind, ...search(view, needle) }).toEqual({ kind, ...expected(elements.length, index) });
+    }
+  });
+
+  // The rows above hold each value once, so indexOf and lastIndexOf agree there.
+  test("a repeated element: indexOf finds the first match, lastIndexOf the last, a wrapped needle neither", () => {
+    const wrapped = 7n + 2n ** 64n;
+    for (const [kind, view] of Object.entries(makeViews(constructor, [7n, 3n, 7n, 7n, 3n]))) {
+      expect({
+        kind,
+        indexOf: view.indexOf(7n),
+        lastIndexOf: view.lastIndexOf(7n),
+        indexOfFrom1: view.indexOf(7n, 1),
+        lastIndexOfFromMinus3: view.lastIndexOf(7n, -3),
+        wrappedIndexOf: view.indexOf(wrapped),
+        wrappedLastIndexOf: view.lastIndexOf(wrapped),
+        wrappedIncludes: view.includes(wrapped),
+      }).toEqual({
+        kind,
+        indexOf: 0,
+        lastIndexOf: 3,
+        indexOfFrom1: 2,
+        lastIndexOfFromMinus3: 2,
+        wrappedIndexOf: -1,
+        wrappedLastIndexOf: -1,
+        wrappedIncludes: false,
+      });
+    }
+  });
+});
+
+test("a Number needle never matches a BigInt element and a BigInt needle never matches a Number element", () => {
+  const i64 = new BigInt64Array([0n, 1n, -1n]);
+  expect(i64.indexOf(1 as any)).toBe(-1);
+  expect(i64.includes(-1 as any)).toBe(false);
+  expect(i64.lastIndexOf("1" as any)).toBe(-1);
+  const u64 = new BigUint64Array([0n, 1n, uint64Max]);
+  expect(u64.indexOf((2 ** 64) as any)).toBe(-1);
+  expect(u64.includes(18446744073709551615 as any)).toBe(false);
+  const f64 = new Float64Array([0, 1, 2 ** 64]);
+  expect(f64.indexOf((2n ** 64n) as any)).toBe(-1);
+  expect(f64.includes(1n as any)).toBe(false);
+});