diff --git a/lib/internal/perf/observe.js b/lib/internal/perf/observe.js
index 91067331aba2c4..c170b14805552e 100644
--- a/lib/internal/perf/observe.js
+++ b/lib/internal/perf/observe.js
@@ -66,6 +66,7 @@ const {
 const { inspect } = require('util');
 
 const { now } = require('internal/perf/utils');
+const { convertToInt } = require('internal/webidl');
 
 const kDispatch = Symbol('kDispatch');
 const kMaybeBuffer = Symbol('kMaybeBuffer');
@@ -430,6 +431,8 @@ function bufferResourceTiming(entry) {
 
 // https://w3c.github.io/resource-timing/#dom-performance-setresourcetimingbuffersize
 function setResourceTimingBufferSize(maxSize) {
+  // unsigned long
+  maxSize = convertToInt('maxSize', maxSize, 32);
   // If the maxSize parameter is less than resource timing buffer current
   // size, no PerformanceResourceTiming objects are to be removed from the
   // performance entry buffer.
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.