diff --git a/packages/compiler-cli/src/metadata/bundle_index_host.ts b/packages/compiler-cli/src/metadata/bundle_index_host.ts
index 17c5bda206..489c32c4db 100644
--- a/packages/compiler-cli/src/metadata/bundle_index_host.ts
+++ b/packages/compiler-cli/src/metadata/bundle_index_host.ts
@@ -71,8 +71,10 @@ export function createBundleIndexHost<H extends ts.CompilerHost>(
     indexFile = files[0];
   } else {
     for (const f of files) {
-      // Assume the shortest file path called index.ts is the entry point
-      if (f.endsWith(path.sep + 'index.ts')) {
+      // Assume the shortest file path called index.ts is the entry point. Note that we
+      // need to use the posix path delimiter here because TypeScript internally only
+      // passes posix paths.
+      if (f.endsWith('/index.ts')) {
         if (!indexFile || indexFile.length > f.length) {
           indexFile = f;
         }