@@ -83,7 +83,7 @@ function evalScript(name, body, breakFirstLine, print, shouldLoadESM = false) {
 
 if (getOptionValue('--experimental-detect-module') &&
 getOptionValue('--input-type') === '' && getOptionValue('--experimental-default-type') === '' &&
-containsModuleSyntax(body, name)) {
+containsModuleSyntax(body, name, null, 'no CJS variables')) {
 return evalModuleEntryPoint(body, print);
 }
 

@@ -1445,7 +1445,8 @@ static MaybeLocal<Function> CompileFunctionForCJSLoader(Environment* env,
 Local<Context> context,
 Local<String> code,
 Local<String> filename,
-bool* cache_rejected) {
+bool* cache_rejected,
+bool is_cjs_scope) {
 Isolate* isolate = context->GetIsolate();
 EscapableHandleScope scope(isolate);
 
@@ -1485,7 +1486,10 @@ static MaybeLocal<Function> CompileFunctionForCJSLoader(Environment* env,
 options = ScriptCompiler::kConsumeCodeCache;
 }
 
-std::vector<Local<String>> params = GetCJSParameters(env->isolate_data());
+std::vector<Local<String>> params;
+if (is_cjs_scope) {
+params = GetCJSParameters(env->isolate_data());
+}
 MaybeLocal<Function> maybe_fn = ScriptCompiler::CompileFunction(
 context,
 &source,
@@ -1544,7 +1548,7 @@ static void CompileFunctionForCJSLoader(
 ShouldNotAbortOnUncaughtScope no_abort_scope(realm->env());
 TryCatchScope try_catch(env);
 if (!CompileFunctionForCJSLoader(
-env, context, code, filename, &cache_rejected)
+env, context, code, filename, &cache_rejected, true)
 .ToLocal(&fn)) {
 CHECK(try_catch.HasCaught());
 CHECK(!try_catch.HasTerminated());
@@ -1682,11 +1686,15 @@ static void ContainsModuleSyntax(const FunctionCallbackInfo<Value>& args) {
 CHECK(args[1]->IsString());
 Local<String> filename = args[1].As<String>();
 
-// Argument 2: resource name (URL for ES module).
+// Argument 3: resource name (URL for ES module).
 Local<String> resource_name = filename;
 if (args[2]->IsString()) {
 resource_name = args[2].As<String>();
 }
+// Argument 4: flag to indicate if CJS variables should not be in scope
+// (they should be for normal CommonJS modules, but not for the
+// CommonJS eval scope).
+bool cjs_var = !args[3]->IsString();
 
 bool cache_rejected = false;
 Local<String> message;
@@ -1695,7 +1703,7 @@ static void ContainsModuleSyntax(const FunctionCallbackInfo<Value>& args) {
 TryCatchScope try_catch(env);
 ShouldNotAbortOnUncaughtScope no_abort_scope(env);
 if (CompileFunctionForCJSLoader(
-env, context, code, filename, &cache_rejected)
+env, context, code, filename, &cache_rejected, cjs_var)
 .ToLocal(&fn)) {
 args.GetReturnValue().Set(false);
 return;

@@ -44,6 +44,19 @@ describe('--experimental-detect-module', { concurrency: true }, () => {
 strictEqual(signal, null);
 });
 
+it('should not switch to module if code is parsable as script', async () => {
+const { code, signal, stdout, stderr } = await spawnPromisified(process.execPath, [
+'--experimental-detect-module',
+'--eval',
+'let __filename,__dirname,require,module,exports;this.a',
+]);
+
+strictEqual(stderr, '');
+strictEqual(stdout, '');
+strictEqual(code, 0);
+strictEqual(signal, null);
+});
+
 it('should be overridden by --experimental-default-type', async () => {
 const { code, signal, stdout, stderr } = await spawnPromisified(process.execPath, [
 '--experimental-detect-module',
@@ -393,3 +406,18 @@ describe('Wrapping a `require` of an ES module while using `--abort-on-uncaught-
 strictEqual(signal, null);
 });
 });
+
+describe('when working with Worker threads', () => {
+it('should support sloppy scripts that declare CJS "global-like" variables', async () => {
+const { code, signal, stdout, stderr } = await spawnPromisified(process.execPath, [
+'--experimental-detect-module',
+'--eval',
+'new worker_threads.Worker("let __filename,__dirname,require,module,exports;this.a",{eval:true})',
+]);
+
+strictEqual(stderr, '');
+strictEqual(stdout, '');
+strictEqual(code, 0);
+strictEqual(signal, null);
+});
+});