diff --git a/packages/npm/date/Date.parse/shim.js b/packages/npm/date/Date.parse/shim.js
index 0e79d3f7..d89acf0f 100644
--- a/packages/npm/date/Date.parse/shim.js
+++ b/packages/npm/date/Date.parse/shim.js
@@ -6,7 +6,7 @@ const { defineProperty: ObjectDefineProperty } = Object
 
 module.exports = function shimDateParse() {
   const polyfill = getPolyfill()
-  if (polyfill && Date.parse !== polyfill) {
+  if (Date.parse !== polyfill) {
     ObjectDefineProperty(Date, 'parse', {
       __proto__: null,
       configurable: true,
diff --git a/packages/npm/es-iterator-helpers/Iterator.prototype.drop/index.js b/packages/npm/es-iterator-helpers/Iterator.prototype.drop/index.js
index 387e6478..0b404192 100644
--- a/packages/npm/es-iterator-helpers/Iterator.prototype.drop/index.js
+++ b/packages/npm/es-iterator-helpers/Iterator.prototype.drop/index.js
@@ -1,6 +1,7 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+const polyfill = getPolyfill()
 
 const desc = value => ({
   __proto__: null,
@@ -11,11 +12,11 @@ const desc = value => ({
 
 module.exports = Object.defineProperties(
   function drop(thisArg, limit = 0) {
-    return new.target ? impl() : Reflect.apply(impl, thisArg, [limit])
+    return new.target ? polyfill() : Reflect.apply(polyfill, thisArg, [limit])
   },
   {
-    getPolyfill: desc(require('./polyfill')),
-    implementation: desc(impl),
+    getPolyfill: desc(getPolyfill),
+    implementation: desc(require('./implementation')),
     shim: desc(require('./shim'))
   }
 )
diff --git a/packages/npm/es-iterator-helpers/Iterator.prototype.filter/index.js b/packages/npm/es-iterator-helpers/Iterator.prototype.filter/index.js
index 74a17d8e..27bbad0d 100644
--- a/packages/npm/es-iterator-helpers/Iterator.prototype.filter/index.js
+++ b/packages/npm/es-iterator-helpers/Iterator.prototype.filter/index.js
@@ -1,6 +1,7 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+const polyfill = getPolyfill()
 
 const desc = value => ({
   __proto__: null,
@@ -11,11 +12,13 @@ const desc = value => ({
 
 module.exports = Object.defineProperties(
   function filter(thisArg, predicate) {
-    return new.target ? new impl() : Reflect.apply(impl, thisArg, [predicate])
+    return new.target
+      ? new polyfill()
+      : Reflect.apply(polyfill, thisArg, [predicate])
   },
   {
-    getPolyfill: desc(require('./polyfill')),
-    implementation: desc(impl),
+    getPolyfill: desc(getPolyfill),
+    implementation: desc(require('./implementation')),
     shim: desc(require('./shim'))
   }
 )
diff --git a/packages/npm/es-iterator-helpers/Iterator.prototype.flatMap/index.js b/packages/npm/es-iterator-helpers/Iterator.prototype.flatMap/index.js
index b18c32b0..cdb536bb 100644
--- a/packages/npm/es-iterator-helpers/Iterator.prototype.flatMap/index.js
+++ b/packages/npm/es-iterator-helpers/Iterator.prototype.flatMap/index.js
@@ -1,6 +1,7 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+const polyfill = getPolyfill()
 
 const desc = value => ({
   __proto__: null,
@@ -11,11 +12,13 @@ const desc = value => ({
 
 module.exports = Object.defineProperties(
   function flatMap(thisArg, mapper) {
-    return new.target ? new impl() : Reflect.apply(impl, thisArg, [mapper])
+    return new.target
+      ? new polyfill()
+      : Reflect.apply(polyfill, thisArg, [mapper])
   },
   {
-    getPolyfill: desc(require('./polyfill')),
-    implementation: desc(impl),
+    getPolyfill: desc(getPolyfill),
+    implementation: desc(require('./implementation')),
     shim: desc(require('./shim'))
   }
 )
diff --git a/packages/npm/es-iterator-helpers/Iterator.prototype.map/index.js b/packages/npm/es-iterator-helpers/Iterator.prototype.map/index.js
index c3a0d794..9f5d935a 100644
--- a/packages/npm/es-iterator-helpers/Iterator.prototype.map/index.js
+++ b/packages/npm/es-iterator-helpers/Iterator.prototype.map/index.js
@@ -1,6 +1,7 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+const polyfill = getPolyfill()
 
 const desc = value => ({
   __proto__: null,
@@ -11,11 +12,13 @@ const desc = value => ({
 
 module.exports = Object.defineProperties(
   function map(thisArg, mapper) {
-    return new.target ? new impl() : Reflect.apply(impl, thisArg, [mapper])
+    return new.target
+      ? new polyfill()
+      : Reflect.apply(polyfill, thisArg, [mapper])
   },
   {
-    getPolyfill: desc(require('./polyfill')),
-    implementation: desc(impl),
+    getPolyfill: desc(getPolyfill),
+    implementation: desc(require('./implementation')),
     shim: desc(require('./shim'))
   }
 )
diff --git a/packages/npm/regexp.prototype.flags/auto.js b/packages/npm/regexp.prototype.flags/auto.js
index 40a8c178..67d3d96d 100644
--- a/packages/npm/regexp.prototype.flags/auto.js
+++ b/packages/npm/regexp.prototype.flags/auto.js
@@ -1 +1,3 @@
-/* empty */
+'use strict'
+
+require('./shim')()
diff --git a/packages/npm/regexp.prototype.flags/implementation.js b/packages/npm/regexp.prototype.flags/implementation.js
index b46adf3e..ad1152da 100644
--- a/packages/npm/regexp.prototype.flags/implementation.js
+++ b/packages/npm/regexp.prototype.flags/implementation.js
@@ -1,3 +1,41 @@
 'use strict'
 
-module.exports = RegExp.prototype.__lookupGetter__('flags')
+const { flagsGetter } = require('./shared')
+
+module.exports = {
+  get flags() {
+    if (new.target || this === null || typeof this !== 'object') {
+      // Defer to builtin flags getter for the error case.
+      return flagsGetter.call(this)
+    }
+    // Flag check order defined as hasIndices, global, ignoreCase, multiline,
+    // dotAll, unicode, unicodeSets, and sticky.
+    // https://tc39.es/ecma262/#sec-get-regexp.prototype.flags
+    let result = ''
+    if (this.hasIndices) {
+      result += 'd'
+    }
+    if (this.global) {
+      result += 'g'
+    }
+    if (this.ignoreCase) {
+      result += 'i'
+    }
+    if (this.multiline) {
+      result += 'm'
+    }
+    if (this.dotAll) {
+      result += 's'
+    }
+    if (this.unicode) {
+      result += 'u'
+    }
+    if (this.unicodeSets) {
+      result += 'v'
+    }
+    if (this.sticky) {
+      result += 'y'
+    }
+    return result
+  }
+}.__lookupGetter__('flags')
diff --git a/packages/npm/regexp.prototype.flags/index.js b/packages/npm/regexp.prototype.flags/index.js
index 6703a57b..d15d2a47 100644
--- a/packages/npm/regexp.prototype.flags/index.js
+++ b/packages/npm/regexp.prototype.flags/index.js
@@ -1,6 +1,7 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+const polyfill = getPolyfill()
 
 const desc = value => ({
   __proto__: null,
@@ -11,11 +12,11 @@ const desc = value => ({
 
 module.exports = Object.defineProperties(
   function flags(thisArg) {
-    return new.target ? new impl() : Reflect.apply(impl, thisArg, [])
+    return new.target ? new polyfill() : Reflect.apply(polyfill, thisArg, [])
   },
   {
-    getPolyfill: desc(require('./polyfill')),
-    implementation: desc(impl),
+    getPolyfill: desc(getPolyfill),
+    implementation: desc(require('./implementation')),
     shim: desc(require('./shim'))
   }
 )
diff --git a/packages/npm/regexp.prototype.flags/polyfill.js b/packages/npm/regexp.prototype.flags/polyfill.js
index ff68a60c..bd9fd025 100644
--- a/packages/npm/regexp.prototype.flags/polyfill.js
+++ b/packages/npm/regexp.prototype.flags/polyfill.js
@@ -1,7 +1,19 @@
 'use strict'
 
 const impl = require('./implementation')
+const { flagsGetter } = require('./shared')
 
 module.exports = function getPolyfill() {
-  return impl
+  let calls = ''
+  flagsGetter.call({
+    // eslint-disable-next-line getter-return
+    get hasIndices() {
+      calls += 'd'
+    },
+    // eslint-disable-next-line getter-return
+    get sticky() {
+      calls += 'y'
+    }
+  })
+  return calls === 'dy' ? flagsGetter : impl
 }
diff --git a/packages/npm/regexp.prototype.flags/shared.d.ts b/packages/npm/regexp.prototype.flags/shared.d.ts
new file mode 100644
index 00000000..45c28818
--- /dev/null
+++ b/packages/npm/regexp.prototype.flags/shared.d.ts
@@ -0,0 +1,5 @@
+declare interface InternalShared {
+  flagsGetter(): string
+}
+declare const shared: InternalShared
+export = shared
diff --git a/packages/npm/regexp.prototype.flags/shared.js b/packages/npm/regexp.prototype.flags/shared.js
new file mode 100644
index 00000000..e3d2e350
--- /dev/null
+++ b/packages/npm/regexp.prototype.flags/shared.js
@@ -0,0 +1,7 @@
+'use strict'
+
+const flagsGetter = RegExp.prototype.__lookupGetter__('flags')
+
+module.exports = {
+  flagsGetter
+}
diff --git a/packages/npm/regexp.prototype.flags/shim.js b/packages/npm/regexp.prototype.flags/shim.js
index c5061d1f..d7e4a37c 100644
--- a/packages/npm/regexp.prototype.flags/shim.js
+++ b/packages/npm/regexp.prototype.flags/shim.js
@@ -1,7 +1,20 @@
 'use strict'
 
-const impl = require('./implementation')
+const getPolyfill = require('./polyfill')
+
+const { defineProperty: ObjectDefineProperty } = Object
+const { __lookupGetter__: ObjectProtoLookupGetter } = Object.prototype
+const { prototype: RegExpPrototype } = RegExp
 
 module.exports = function shimRegExpProtoFlags() {
-  return impl
+  const polyfill = getPolyfill()
+  if (ObjectProtoLookupGetter.call(RegExpPrototype, 'flags') !== polyfill) {
+    ObjectDefineProperty(RegExpPrototype, 'flags', {
+      __proto__: null,
+      configurable: true,
+      enumerable: false,
+      get: polyfill
+    })
+  }
+  return polyfill
 }
diff --git a/scripts/constants.js b/scripts/constants.js
index 5c959ad2..88fa7ae9 100644
--- a/scripts/constants.js
+++ b/scripts/constants.js
@@ -328,7 +328,7 @@ const lazyPrettierConfigPromise = () =>
   prettier.resolveConfig(prettierConfigPath, { editorconfig: true })
 const lazyPrettierIgnoreFile = () => includeIgnoreFile(prettierIgnorePath)
 const lazyRunScriptParallelExecPath = () => whichSync('run-p')
-const lazyTapRunExecPath = () => whichSync('tap-run')
+const lazyTapExecPath = () => whichSync('tap')
 
 const copyLeftLicenses = new Set([
   'AGPL-3.0-or-later',
@@ -526,7 +526,7 @@ const constants = Object.freeze(
       rootTapConfigPath,
       rootTsConfigPath,
       runScriptParallelExecPath: undefined,
-      tapRunExecPath: undefined,
+      tapExecPath: undefined,
       templatesPath,
       testNpmPath,
       testNpmPkgJsonPath,
@@ -551,7 +551,7 @@ const constants = Object.freeze(
       npmPackageNames: lazyNpmPackageNames,
       prettierConfigPromise: lazyPrettierConfigPromise,
       prettierIgnoreFile: lazyPrettierIgnoreFile,
-      tapRunExecPath: lazyTapRunExecPath,
+      tapExecPath: lazyTapExecPath,
       runScriptParallelExecPath: lazyRunScriptParallelExecPath
     }
   )
diff --git a/scripts/make-npm-package.js b/scripts/make-npm-package.js
index 161b91ad..11952ff4 100644
--- a/scripts/make-npm-package.js
+++ b/scripts/make-npm-package.js
@@ -425,7 +425,6 @@ function toChoice(value) {
       ],
       {
         cwd: rootPath,
-        shell: true,
         stdio: 'inherit'
       }
     )
diff --git a/scripts/tap.js b/scripts/tap.js
index 3b52504d..dfb66171 100644
--- a/scripts/tap.js
+++ b/scripts/tap.js
@@ -6,12 +6,11 @@ const { runBin } = require('@socketregistry/scripts/utils/npm')
 
 ;(async () => {
   await runBin(
-    // Lazily access constants.tapRunExecPath.
-    constants.tapRunExecPath,
+    // Lazily access constants.tapExecPath.
+    constants.tapExecPath,
     process.argv.slice(2),
     {
       cwd: rootPath,
-      shell: true,
       stdio: 'inherit',
       env: {
         __proto__: null,
diff --git a/scripts/utils/npm.js b/scripts/utils/npm.js
index 9bdde1d6..aef46fa6 100644
--- a/scripts/utils/npm.js
+++ b/scripts/utils/npm.js
@@ -25,7 +25,11 @@ async function runBin(binPath, args, options) {
   return await spawn(
     WIN_32 ? binPath : execPath,
     [...(WIN_32 ? [] : [binPath]), ...args],
-    options
+    {
+      __proto__: null,
+      ...options,
+      shell: true,
+    }
   )
 }
 
diff --git a/test/packages.test.ts b/test/packages.test.ts
index 9fabf6a3..fac3d234 100644
--- a/test/packages.test.ts
+++ b/test/packages.test.ts
@@ -1,3 +1,4 @@
+import assertLoose from 'node:assert'
 import assert from 'node:assert/strict'
 import { createRequire } from 'node:module'
 import path from 'node:path'
@@ -314,12 +315,17 @@ for (const eco of constants.ecosystems) {
                 assert.ok(shimApiKeys.every(k => mainKeys.includes(k)))
               })
 
-              it('getPolyfill() === implementation', async t => {
+              it('getPolyfill() is like implementation', async t => {
                 if (skipping) return t.skip(skipMessage)
-                assert.strictEqual(
-                  req('./polyfill.js')(),
-                  req('./implementation.js')
-                )
+                const impl = req('./implementation.js')
+                const polyfill = req('./polyfill.js')()
+                assert.strictEqual(typeof impl, typeof polyfill)
+                if (typeof impl === 'function') {
+                  assert.strictEqual(impl.name, polyfill.name)
+                  assert.strictEqual(impl.length, polyfill.length)
+                } else {
+                  assertLoose.equal(impl, polyfill)
+                }
               })
             })
           }