diff --git a/packages/language-service/src/typescript_host.ts b/packages/language-service/src/typescript_host.ts
index 5bc657e0cc..934501daf9 100644
--- a/packages/language-service/src/typescript_host.ts
+++ b/packages/language-service/src/typescript_host.ts
@@ -62,7 +62,12 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
   private readonly staticSymbolResolver: StaticSymbolResolver;
 
   private readonly staticSymbolCache = new StaticSymbolCache();
-  private readonly fileToComponent = new Map<string, StaticSymbol>();
+  /**
+   * Key of the `fileToComponent` map must be TS internal normalized path (path
+   * separator must be `/`), value of the map is the StaticSymbol for the
+   * Component class declaration.
+   */
+  private readonly fileToComponent = new Map<ts.server.NormalizedPath, StaticSymbol>();
   private readonly collectedErrors = new Map<string, any[]>();
   private readonly fileVersions = new Map<string, string>();
   private readonly urlResolver: UrlResolver;
@@ -165,7 +170,7 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
   /**
    * Return all known external templates.
    */
-  getExternalTemplates(): string[] {
+  getExternalTemplates(): ts.server.NormalizedPath[] {
     return [...this.fileToComponent.keys()];
   }
 
@@ -210,7 +215,7 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
           const templateName = this.urlResolver.resolve(
               this.reflector.componentModuleUrl(directive.reference),
               metadata.template.templateUrl);
-          this.fileToComponent.set(templateName, directive.reference);
+          this.fileToComponent.set(tss.server.toNormalizedPath(templateName), directive.reference);
         }
       }
     }
@@ -417,7 +422,7 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
     }
     const source = snapshot.getText(0, snapshot.getLength());
     // Next find the component class symbol
-    const classSymbol = this.fileToComponent.get(fileName);
+    const classSymbol = this.fileToComponent.get(tss.server.toNormalizedPath(fileName));
     if (!classSymbol) {
       return;
     }
diff --git a/packages/language-service/test/typescript_host_spec.ts b/packages/language-service/test/typescript_host_spec.ts
index f1bab4d1bc..ee4b7ed69c 100644
--- a/packages/language-service/test/typescript_host_spec.ts
+++ b/packages/language-service/test/typescript_host_spec.ts
@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import * as path from 'path';
 import * as ts from 'typescript';
 
 import {TypeScriptServiceHost} from '../src/typescript_host';
@@ -114,7 +115,7 @@ describe('TypeScriptServiceHost', () => {
     const tsLS = ts.createLanguageService(tsLSHost);
     const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
     ngLSHost.getAnalyzedModules();
-    expect(ngLSHost.getExternalTemplates()).toContain('/app/#inner/inner.html');
+    expect(ngLSHost.getExternalTemplates() as string[]).toContain('/app/#inner/inner.html');
   });
 
   // https://github.com/angular/angular/issues/32301
@@ -238,7 +239,7 @@ describe('TypeScriptServiceHost', () => {
     let content = `
     import {CommonModule} from '@angular/common';
     import {NgModule} from '@angular/core';
-    
+
     @NgModule({
       entryComponents: [CommonModule],
     })
@@ -256,7 +257,7 @@ describe('TypeScriptServiceHost', () => {
     content = `
     import {CommonModule} from '@angular/common';
     import {NgModule} from '@angular/core';
-    
+
     @NgModule({})
     export class AppModule {}
     `;
@@ -265,4 +266,19 @@ describe('TypeScriptServiceHost', () => {
     newModules = ngLSHost.getAnalyzedModules();
     expect(newModules.ngModules.length).toBeGreaterThan(0);
   });
+
+  it('should normalize path on Windows', () => {
+    // Spy on the `path.resolve()` method called by the URL resolver and mimic
+    // behavior on Windows.
+    spyOn(path, 'resolve').and.callFake((...pathSegments: string[]) => {
+      return path.win32.resolve(...pathSegments);
+    });
+    const tsLSHost = new MockTypescriptHost(['/app/main.ts']);
+    const tsLS = ts.createLanguageService(tsLSHost);
+    const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
+    ngLSHost.getAnalyzedModules();
+    const externalTemplates: string[] = ngLSHost.getExternalTemplates();
+    // External templates should be normalized.
+    expect(externalTemplates).toContain('/app/test.ng');
+  });
 });