diff --git a/lib/internal/cluster/primary.js b/lib/internal/cluster/primary.js
index 9eeb2735857bec..cc389949079b4e 100644
--- a/lib/internal/cluster/primary.js
+++ b/lib/internal/cluster/primary.js
@@ -6,10 +6,14 @@ const {
   ArrayPrototypeSome,
   ObjectKeys,
   ObjectValues,
-  RegExpPrototypeExec,
   SafeMap,
   StringPrototypeStartsWith,
 } = primordials;
+const {
+  codes: {
+    ERR_SOCKET_BAD_PORT,
+  }
+} = require('internal/errors');
 
 const assert = require('internal/assert');
 const { fork } = require('child_process');
@@ -18,14 +22,12 @@ const EventEmitter = require('events');
 const RoundRobinHandle = require('internal/cluster/round_robin_handle');
 const SharedHandle = require('internal/cluster/shared_handle');
 const Worker = require('internal/cluster/worker');
+const { getInspectPort, isUsingInspector } = require('internal/util/inspector');
 const { internal, sendHelper } = require('internal/cluster/utils');
 const cluster = new EventEmitter();
 const intercom = new EventEmitter();
 const SCHED_NONE = 1;
 const SCHED_RR = 2;
-const minPort = 1024;
-const maxPort = 65535;
-const { validatePort } = require('internal/validators');
 
 module.exports = cluster;
 
@@ -40,7 +42,6 @@ cluster.SCHED_NONE = SCHED_NONE;  // Leave it to the operating system.
 cluster.SCHED_RR = SCHED_RR;      // Primary distributes connections.
 
 let ids = 0;
-let debugPortOffset = 1;
 let initialized = false;
 
 // XXX(bnoordhuis) Fold cluster.schedulingPolicy into cluster.settings?
@@ -117,29 +118,12 @@ function setupSettingsNT(settings) {
 function createWorkerProcess(id, env) {
   const workerEnv = { ...process.env, ...env, NODE_UNIQUE_ID: `${id}` };
   const execArgv = [...cluster.settings.execArgv];
-  const debugArgRegex = /--inspect(?:-brk|-port)?|--debug-port/;
-  const nodeOptions = process.env.NODE_OPTIONS || '';
-
-  // TODO(MoLow): Use getInspectPort from internal/util/inspector
-  if (ArrayPrototypeSome(execArgv,
-                         (arg) => RegExpPrototypeExec(debugArgRegex, arg) !== null) ||
-      RegExpPrototypeExec(debugArgRegex, nodeOptions) !== null) {
-    let inspectPort;
-    if ('inspectPort' in cluster.settings) {
-      if (typeof cluster.settings.inspectPort === 'function')
-        inspectPort = cluster.settings.inspectPort();
-      else
-        inspectPort = cluster.settings.inspectPort;
-
-      validatePort(inspectPort);
-    } else {
-      inspectPort = process.debugPort + debugPortOffset;
-      if (inspectPort > maxPort)
-        inspectPort = inspectPort - maxPort + minPort - 1;
-      debugPortOffset++;
-    }
 
-    ArrayPrototypePush(execArgv, `--inspect-port=${inspectPort}`);
+  if (cluster.settings.inspectPort === null) {
+    throw new ERR_SOCKET_BAD_PORT('Port', null, true);
+  }
+  if (isUsingInspector(cluster.settings.execArgv)) {
+    ArrayPrototypePush(execArgv, `--inspect-port=${getInspectPort(cluster.settings.inspectPort)}`);
   }
 
   return fork(cluster.settings.exec, cluster.settings.args, {
diff --git a/lib/internal/util/inspector.js b/lib/internal/util/inspector.js
index e24c4e0ad35124..038479b173ceaf 100644
--- a/lib/internal/util/inspector.js
+++ b/lib/internal/util/inspector.js
@@ -8,6 +8,7 @@ const {
   ObjectKeys,
   ObjectPrototypeHasOwnProperty,
   RegExpPrototypeExec,
+  SafeWeakMap,
 } = primordials;
 
 const { validatePort } = require('internal/validators');
@@ -17,19 +18,18 @@ const kMaxPort = 65535;
 const kInspectArgRegex = /--inspect(?:-brk|-port)?|--debug-port/;
 const kInspectMsgRegex = /Debugger listening on ws:\/\/\[?(.+?)\]?:(\d+)\/|Debugger attached|Waiting for the debugger to disconnect\.\.\./;
 
-let _isUsingInspector;
-function isUsingInspector() {
-  _isUsingInspector ??=
-    ArrayPrototypeSome(process.execArgv, (arg) => RegExpPrototypeExec(kInspectArgRegex, arg) !== null) ||
-    RegExpPrototypeExec(kInspectArgRegex, process.env.NODE_OPTIONS) !== null;
-  return _isUsingInspector;
+const _isUsingInspector = new SafeWeakMap();
+function isUsingInspector(execArgv = process.execArgv) {
+  if (!_isUsingInspector.has(execArgv)) {
+    _isUsingInspector.set(execArgv,
+                          ArrayPrototypeSome(execArgv, (arg) => RegExpPrototypeExec(kInspectArgRegex, arg) !== null) ||
+      RegExpPrototypeExec(kInspectArgRegex, process.env.NODE_OPTIONS) !== null);
+  }
+  return _isUsingInspector.get(execArgv);
 }
 
 let debugPortOffset = 1;
 function getInspectPort(inspectPort) {
-  if (!isUsingInspector()) {
-    return null;
-  }
   if (typeof inspectPort === 'function') {
     inspectPort = inspectPort();
   } else if (inspectPort == null) {