diff --git a/packages/language-service/ivy/language_service.ts b/packages/language-service/ivy/language_service.ts
index 2a6903bf65..8d8989f958 100644
--- a/packages/language-service/ivy/language_service.ts
+++ b/packages/language-service/ivy/language_service.ts
@@ -242,9 +242,11 @@ function getOrCreateTypeCheckScriptInfo(
     // attempt to fetch the content from disk and fail.
     scriptInfo = projectService.getOrCreateScriptInfoForNormalizedPath(
         ts.server.toNormalizedPath(tcf),
-        true,              // openedByClient
-        '',                // fileContent
-        ts.ScriptKind.TS,  // scriptKind
+        true,  // openedByClient
+        '',    // fileContent
+        // script info added by plugins should be marked as external, see
+        // https://github.com/microsoft/TypeScript/blob/b217f22e798c781f55d17da72ed099a9dee5c650/src/compiler/program.ts#L1897-L1899
+        ts.ScriptKind.External,  // scriptKind
     );
     if (!scriptInfo) {
       throw new Error(`Failed to create script info for ${tcf}`);
diff --git a/packages/language-service/ivy/test/legacy/mock_host.ts b/packages/language-service/ivy/test/legacy/mock_host.ts
index f1b6f3f4e0..d825907e41 100644
--- a/packages/language-service/ivy/test/legacy/mock_host.ts
+++ b/packages/language-service/ivy/test/legacy/mock_host.ts
@@ -243,9 +243,9 @@ export class MockService {
     }
     const newScriptInfo = this.ps.getOrCreateScriptInfoForNormalizedPath(
         ts.server.toNormalizedPath(fileName),
-        true,                    // openedByClient
-        '',                      // fileContent
-        ts.ScriptKind.External,  // scriptKind
+        true,                   // openedByClient
+        '',                     // fileContent
+        ts.ScriptKind.Unknown,  // scriptKind
     );
     if (!newScriptInfo) {
       throw new Error(`Failed to create new script info for ${fileName}`);
diff --git a/packages/language-service/ivy/test/legacy/ts_plugin_spec.ts b/packages/language-service/ivy/test/legacy/ts_plugin_spec.ts
new file mode 100644
index 0000000000..ce6f75fc75
--- /dev/null
+++ b/packages/language-service/ivy/test/legacy/ts_plugin_spec.ts
@@ -0,0 +1,29 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {LanguageService} from '../../language_service';
+import {getExternalFiles} from '../../ts_plugin';
+
+import {APP_COMPONENT, setup} from './mock_host';
+
+describe('getExternalFiles()', () => {
+  it('should return all typecheck files', () => {
+    const {project, tsLS} = setup();
+    let externalFiles = getExternalFiles(project);
+    // Initially there are no external files because Ivy compiler hasn't done
+    // a global analysis
+    expect(externalFiles).toEqual([]);
+    // Trigger global analysis
+    const ngLS = new LanguageService(project, tsLS);
+    ngLS.getSemanticDiagnostics(APP_COMPONENT);
+    // Now that global analysis is run, we should have all the typecheck files
+    externalFiles = getExternalFiles(project);
+    expect(externalFiles.length).toBe(1);
+    expect(externalFiles[0].endsWith('app.component.ngtypecheck.ts')).toBeTrue();
+  });
+});
diff --git a/packages/language-service/ivy/ts_plugin.ts b/packages/language-service/ivy/ts_plugin.ts
index c21a04da47..b48adc87bd 100644
--- a/packages/language-service/ivy/ts_plugin.ts
+++ b/packages/language-service/ivy/ts_plugin.ts
@@ -120,3 +120,19 @@ export function create(info: ts.server.PluginCreateInfo): ts.LanguageService {
     getCompletionEntrySymbol,
   };
 }
+
+export function getExternalFiles(project: ts.server.Project): string[] {
+  if (!project.hasRoots()) {
+    return [];  // project has not been initialized
+  }
+  const typecheckFiles: string[] = [];
+  for (const scriptInfo of project.getScriptInfos()) {
+    if (scriptInfo.scriptKind === ts.ScriptKind.External) {
+      // script info for typecheck file is marked as external, see
+      // getOrCreateTypeCheckScriptInfo() in
+      // packages/language-service/ivy/language_service.ts
+      typecheckFiles.push(scriptInfo.fileName);
+    }
+  }
+  return typecheckFiles;
+}