diff --git a/packages/angular/build/src/tools/esbuild/stylesheets/sass-language.ts b/packages/angular/build/src/tools/esbuild/stylesheets/sass-language.ts
index 3939e63b9035..cce85f61b9a2 100644
--- a/packages/angular/build/src/tools/esbuild/stylesheets/sass-language.ts
+++ b/packages/angular/build/src/tools/esbuild/stylesheets/sass-language.ts
@@ -69,6 +69,20 @@ export const SassStylesheetLanguage = Object.freeze<StylesheetLanguage>({
   },
 });
 
+export function isPackageUrl(url: string): boolean {
+  if (url.startsWith('pkg:')) {
+    return true;
+  }
+
+  return (
+    url.length > 0 &&
+    !url.startsWith('.') &&
+    !url.startsWith('/') &&
+    !url.startsWith('\\') &&
+    !url.includes(':')
+  );
+}
+
 function parsePackageName(url: string): { packageName: string; readonly pathSegments: string[] } {
   const parts = (url.startsWith('pkg:') ? url.slice(4) : url).split('/');
   const hasScope = parts.length >= 2 && parts[0][0] === '@';
@@ -131,9 +145,8 @@ async function compileString(
       importers: [
         {
           findFileUrl: (url, options) => {
-            const cacheKey = url.startsWith('pkg:')
-              ? url
-              : `${options.containingUrl?.href ?? ''}:${url}`;
+            const isPackage = isPackageUrl(url);
+            const cacheKey = isPackage ? url : `${options.containingUrl?.href ?? ''}:${url}`;
 
             return currentResolutionCache.getOrCreate(cacheKey, async () => {
               const result = await resolveUrl(url, options);
@@ -142,13 +155,16 @@ async function compileString(
               }
 
               // Check for package deep imports
+              if (!isPackage) {
+                return null;
+              }
+
               const { packageName, pathSegments } = parsePackageName(url);
 
               // Caching package root locations is particularly beneficial for `@material/*` packages
               // which extensively use deep imports.
-              const packageRootKey = `${options.containingUrl?.href ?? ''}:${packageName}`;
               const packageRoot = await currentPackageRootCache.getOrCreate(
-                packageRootKey,
+                packageName,
                 async () => {
                   // Use the required presence of a package root `package.json` file to resolve the location
                   const packageResult = await resolveUrl(packageName + '/package.json', options);
diff --git a/packages/angular/build/src/tools/esbuild/stylesheets/sass-language_spec.ts b/packages/angular/build/src/tools/esbuild/stylesheets/sass-language_spec.ts
new file mode 100644
index 000000000000..7be104741caa
--- /dev/null
+++ b/packages/angular/build/src/tools/esbuild/stylesheets/sass-language_spec.ts
@@ -0,0 +1,49 @@
+/**
+ * @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.dev/license
+ */
+
+import { isPackageUrl } from './sass-language';
+
+describe('sass-language', () => {
+  describe('isPackageUrl', () => {
+    it('should identify pkg: scheme URLs as package URLs', () => {
+      expect(isPackageUrl('pkg:@angular/material')).toBeTrue();
+      expect(isPackageUrl('pkg:bootstrap')).toBeTrue();
+      expect(isPackageUrl('pkg:@material/button/button')).toBeTrue();
+    });
+
+    it('should identify bare specifiers as package URLs', () => {
+      expect(isPackageUrl('@angular/material')).toBeTrue();
+      expect(isPackageUrl('@angular/material/button')).toBeTrue();
+      expect(isPackageUrl('@material/button/button.scss')).toBeTrue();
+      expect(isPackageUrl('bootstrap')).toBeTrue();
+      expect(isPackageUrl('bootstrap/scss/bootstrap')).toBeTrue();
+    });
+
+    it('should not identify relative paths as package URLs', () => {
+      expect(isPackageUrl('./styles.scss')).toBeFalse();
+      expect(isPackageUrl('../shared/variables')).toBeFalse();
+      expect(isPackageUrl('.hidden')).toBeFalse();
+      expect(isPackageUrl('.\\styles.scss')).toBeFalse();
+      expect(isPackageUrl('..\\shared\\variables')).toBeFalse();
+    });
+
+    it('should not identify absolute paths or non-pkg URLs as package URLs', () => {
+      expect(isPackageUrl('/styles/theme.scss')).toBeFalse();
+      expect(isPackageUrl('\\styles\\theme.scss')).toBeFalse();
+      expect(isPackageUrl('file:///path/to/theme.scss')).toBeFalse();
+      expect(isPackageUrl('http://example.com/styles.css')).toBeFalse();
+      expect(isPackageUrl('https://example.com/styles.css')).toBeFalse();
+      expect(isPackageUrl('C:\\path\\to\\theme.scss')).toBeFalse();
+      expect(isPackageUrl('C:/path/to/theme.scss')).toBeFalse();
+    });
+
+    it('should not identify empty string as a package URL', () => {
+      expect(isPackageUrl('')).toBeFalse();
+    });
+  });
+});