diff --git a/lib/internal/perf/performance.js b/lib/internal/perf/performance.js
index 0053ec23a7afcb..77c8c7ae1c4904 100644
--- a/lib/internal/perf/performance.js
+++ b/lib/internal/perf/performance.js
@@ -44,6 +44,7 @@ const timerify = require('internal/perf/timerify');
 const { customInspectSymbol: kInspect, kEnumerableProperty, kEmptyObject } = require('internal/util');
 const { inspect } = require('util');
 const { validateInternalField } = require('internal/validators');
+const { convertToInt } = require('internal/webidl');
 
 const {
   getTimeOriginTimestamp
@@ -144,6 +145,8 @@ class Performance extends EventTarget {
     if (arguments.length === 0) {
       throw new ERR_MISSING_ARGS('maxSize');
     }
+    // unsigned long
+    maxSize = convertToInt('maxSize', maxSize, 32);
     return setResourceTimingBufferSize(maxSize);
   }
 
diff --git a/lib/internal/webidl.js b/lib/internal/webidl.js
new file mode 100644
index 00000000000000..66edd63ca16a65
--- /dev/null
+++ b/lib/internal/webidl.js
@@ -0,0 +1,163 @@
+'use strict';
+
+const {
+  MathAbs,
+  MathMax,
+  MathMin,
+  MathPow,
+  MathSign,
+  MathTrunc,
+  NumberIsNaN,
+  NumberMAX_SAFE_INTEGER,
+  NumberMIN_SAFE_INTEGER,
+} = primordials;
+
+const {
+  codes: {
+    ERR_INVALID_ARG_VALUE,
+  },
+} = require('internal/errors');
+const { kEmptyObject } = require('internal/util');
+
+// https://webidl.spec.whatwg.org/#abstract-opdef-integerpart
+const integerPart = MathTrunc;
+
+/* eslint-disable node-core/non-ascii-character */
+// Round x to the nearest integer, choosing the even integer if it lies halfway
+// between two, and choosing +0 rather than -0.
+// This is different from Math.round, which rounds to the next integer in the
+// direction of +∞ when the fraction portion is exactly 0.5.
+/* eslint-enable node-core/non-ascii-character */
+function evenRound(x) {
+  // Convert -0 to +0.
+  const i = integerPart(x) + 0;
+  const reminder = MathAbs(x % 1);
+  const sign = MathSign(i);
+  if (reminder === 0.5) {
+    return i % 2 === 0 ? i : i + sign;
+  }
+  const r = reminder < 0.5 ? i : i + sign;
+  // Convert -0 to +0.
+  if (r === 0) {
+    return 0;
+  }
+  return r;
+}
+
+function pow2(exponent) {
+  // << operates on 32 bit signed integers.
+  if (exponent < 31) {
+    return 1 << exponent;
+  }
+  if (exponent === 31) {
+    return 0x8000_0000;
+  }
+  if (exponent === 32) {
+    return 0x1_0000_0000;
+  }
+  return MathPow(2, exponent);
+}
+
+// https://tc39.es/ecma262/#eqn-modulo
+// The notation “x modulo y” computes a value k of the same sign as y.
+function modulo(x, y) {
+  const r = x % y;
+  // Convert -0 to +0.
+  if (r === 0) {
+    return 0;
+  }
+  return r;
+}
+
+// https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
+function convertToInt(name, value, bitLength, options = kEmptyObject) {
+  const { signed = false, enforceRange = false, clamp = false } = options;
+
+  let upperBound;
+  let lowerBound;
+  // 1. If bitLength is 64, then:
+  if (bitLength === 64) {
+    // 1.1. Let upperBound be 2^53 − 1.
+    upperBound = NumberMAX_SAFE_INTEGER;
+    // 1.2. If signedness is "unsigned", then let lowerBound be 0.
+    // 1.3. Otherwise let lowerBound be −2^53 + 1.
+    lowerBound = !signed ? 0 : NumberMIN_SAFE_INTEGER;
+  } else if (!signed) {
+    // 2. Otherwise, if signedness is "unsigned", then:
+    // 2.1. Let lowerBound be 0.
+    // 2.2. Let upperBound be 2^bitLength − 1.
+    lowerBound = 0;
+    upperBound = pow2(bitLength) - 1;
+  } else {
+    // 3. Otherwise:
+    // 3.1. Let lowerBound be -2^(bitLength − 1).
+    // 3.2. Let upperBound be 2^(bitLength − 1) − 1.
+    lowerBound = -pow2(bitLength - 1);
+    upperBound = pow2(bitLength - 1) - 1;
+  }
+
+  // 4. Let x be ? ToNumber(V).
+  let x = +value;
+  // 5. If x is −0, then set x to +0.
+  if (x === 0) {
+    x = 0;
+  }
+
+  // 6. If the conversion is to an IDL type associated with the [EnforceRange]
+  // extended attribute, then:
+  if (enforceRange) {
+    // 6.1. If x is NaN, +∞, or −∞, then throw a TypeError.
+    if (NumberIsNaN(x) || x === Infinity || x === -Infinity) {
+      throw new ERR_INVALID_ARG_VALUE(name, x);
+    }
+    // 6.2. Set x to IntegerPart(x).
+    x = integerPart(x);
+
+    // 6.3. If x < lowerBound or x > upperBound, then throw a TypeError.
+    if (x < lowerBound || x > upperBound) {
+      throw new ERR_INVALID_ARG_VALUE(name, x);
+    }
+
+    // 6.4. Return x.
+    return x;
+  }
+
+  // 7. If x is not NaN and the conversion is to an IDL type associated with
+  // the [Clamp] extended attribute, then:
+  if (clamp && !NumberIsNaN(x)) {
+    // 7.1. Set x to min(max(x, lowerBound), upperBound).
+    x = MathMin(MathMax(x, lowerBound), upperBound);
+
+    // 7.2. Round x to the nearest integer, choosing the even integer if it
+    // lies halfway between two, and choosing +0 rather than −0.
+    x = evenRound(x);
+
+    // 7.3. Return x.
+    return x;
+  }
+
+  // 8. If x is NaN, +0, +∞, or −∞, then return +0.
+  if (NumberIsNaN(x) || x === 0 || x === Infinity || x === -Infinity) {
+    return 0;
+  }
+
+  // 9. Set x to IntegerPart(x).
+  x = integerPart(x);
+
+  // 10. Set x to x modulo 2^bitLength.
+  x = modulo(x, pow2(bitLength));
+
+  // 11. If signedness is "signed" and x ≥ 2^(bitLength − 1), then return x −
+  // 2^bitLength.
+  if (signed && x >= pow2(bitLength - 1)) {
+    return x - pow2(bitLength);
+  }
+
+  // 12. Otherwise, return x.
+  return x;
+}
+
+module.exports = {
+  convertToInt,
+  evenRound,
+};
diff --git a/test/parallel/test-bootstrap-modules.js b/test/parallel/test-bootstrap-modules.js
index ae8dcf315d5131..577db94c6eb9b8 100644
--- a/test/parallel/test-bootstrap-modules.js
+++ b/test/parallel/test-bootstrap-modules.js
@@ -149,6 +149,7 @@ const expectedModules = new Set([
   'NativeModule internal/validators',
   'NativeModule internal/vm/module',
   'NativeModule internal/wasm_web_api',
+  'NativeModule internal/webidl',
   'NativeModule internal/webstreams/adapters',
   'NativeModule internal/webstreams/compression',
   'NativeModule internal/webstreams/encoding',
diff --git a/test/parallel/test-internal-webidl-converttoint.js b/test/parallel/test-internal-webidl-converttoint.js
new file mode 100644
index 00000000000000..7e7c024387a0ec
--- /dev/null
+++ b/test/parallel/test-internal-webidl-converttoint.js
@@ -0,0 +1,58 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { convertToInt, evenRound } = require('internal/webidl');
+
+assert.strictEqual(evenRound(-0.5), 0);
+assert.strictEqual(evenRound(0.5), 0);
+assert.strictEqual(evenRound(-1.5), -2);
+assert.strictEqual(evenRound(1.5), 2);
+assert.strictEqual(evenRound(3.4), 3);
+assert.strictEqual(evenRound(4.6), 5);
+assert.strictEqual(evenRound(5), 5);
+assert.strictEqual(evenRound(6), 6);
+
+// https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
+assert.strictEqual(convertToInt('x', 0, 64), 0);
+assert.strictEqual(convertToInt('x', 1, 64), 1);
+assert.strictEqual(convertToInt('x', -0.5, 64), 0);
+assert.strictEqual(convertToInt('x', -0.5, 64, { signed: true }), 0);
+assert.strictEqual(convertToInt('x', -1.5, 64, { signed: true }), -1);
+
+// EnforceRange
+const OutOfRangeValues = [ NaN, Infinity, -Infinity, 2 ** 53, -(2 ** 53) ];
+for (const value of OutOfRangeValues) {
+  assert.throws(() => convertToInt('x', value, 64, { enforceRange: true }), {
+    name: 'TypeError',
+    code: 'ERR_INVALID_ARG_VALUE',
+  });
+}
+
+// Out of range: clamp
+assert.strictEqual(convertToInt('x', NaN, 64, { clamp: true }), 0);
+assert.strictEqual(convertToInt('x', Infinity, 64, { clamp: true }), Number.MAX_SAFE_INTEGER);
+assert.strictEqual(convertToInt('x', -Infinity, 64, { clamp: true }), 0);
+assert.strictEqual(convertToInt('x', -Infinity, 64, { signed: true, clamp: true }), Number.MIN_SAFE_INTEGER);
+assert.strictEqual(convertToInt('x', 0x1_0000_0000, 32, { clamp: true }), 0xFFFF_FFFF);
+assert.strictEqual(convertToInt('x', 0xFFFF_FFFF, 32, { clamp: true }), 0xFFFF_FFFF);
+assert.strictEqual(convertToInt('x', 0x8000_0000, 32, { clamp: true, signed: true }), 0x7FFF_FFFF);
+assert.strictEqual(convertToInt('x', 0xFFFF_FFFF, 32, { clamp: true, signed: true }), 0x7FFF_FFFF);
+assert.strictEqual(convertToInt('x', 0.5, 64, { clamp: true }), 0);
+assert.strictEqual(convertToInt('x', 1.5, 64, { clamp: true }), 2);
+assert.strictEqual(convertToInt('x', -0.5, 64, { clamp: true }), 0);
+assert.strictEqual(convertToInt('x', -0.5, 64, { signed: true, clamp: true }), 0);
+assert.strictEqual(convertToInt('x', -1.5, 64, { signed: true, clamp: true }), -2);
+
+// Out of range, step 8.
+assert.strictEqual(convertToInt('x', NaN, 64), 0);
+assert.strictEqual(convertToInt('x', Infinity, 64), 0);
+assert.strictEqual(convertToInt('x', -Infinity, 64), 0);
+assert.strictEqual(convertToInt('x', 0x1_0000_0000, 32), 0);
+assert.strictEqual(convertToInt('x', 0x1_0000_0001, 32), 1);
+assert.strictEqual(convertToInt('x', 0xFFFF_FFFF, 32), 0xFFFF_FFFF);
+
+// Out of range, step 11.
+assert.strictEqual(convertToInt('x', 0x8000_0000, 32, { signed: true }), -0x8000_0000);
+assert.strictEqual(convertToInt('x', 0xFFF_FFFF, 32, { signed: true }), 0xFFF_FFFF);
diff --git a/test/parallel/test-performance-resourcetimingbuffersize.js b/test/parallel/test-performance-resourcetimingbuffersize.js
index eba46fa3ce95e0..3b9e77799b3b25 100644
--- a/test/parallel/test-performance-resourcetimingbuffersize.js
+++ b/test/parallel/test-performance-resourcetimingbuffersize.js
@@ -30,6 +30,17 @@ const initiatorType = '';
 const cacheMode = '';
 
 async function main() {
+  // Invalid buffer size values are converted to 0.
+  const invalidValues = [ null, undefined, true, false, -1, 0.5, Infinity, NaN, '', 'foo', {}, [], () => {} ];
+  for (const value of invalidValues) {
+    performance.setResourceTimingBufferSize(value);
+    performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, globalThis, cacheMode);
+    assert.strictEqual(performance.getEntriesByType('resource').length, 0);
+    performance.clearResourceTimings();
+  }
+  // Wait for the buffer full event to be cleared.
+  await waitBufferFullEvent();
+
   performance.setResourceTimingBufferSize(1);
   performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, globalThis, cacheMode);
   // Trigger a resourcetimingbufferfull event.