diff --git a/packages/bazel/src/modify_tsconfig.js b/packages/bazel/src/modify_tsconfig.js
index 7eee260c2f..b93fd97636 100644
--- a/packages/bazel/src/modify_tsconfig.js
+++ b/packages/bazel/src/modify_tsconfig.js
@@ -23,13 +23,19 @@ function main(args) {
   const data = JSON.parse(fs.readFileSync(input, {encoding: 'utf-8'}));
   data['compilerOptions']['target'] = 'es5';
   data['bazelOptions']['es5Mode'] = true;
-  data['compilerOptions']['outDir'] = path.join(data['compilerOptions']['outDir'], newRoot);
+  data['compilerOptions']['outDir'] = path.posix.join(data['compilerOptions']['outDir'], newRoot);
   if (data['angularCompilerOptions']) {
+    // Relative path to the execroot that refers to the directory for the ES5 output files.
+    const newOutputBase = path.posix.join(binDir, newRoot);
     // Don't enable tsickle's closure conversions
     data['angularCompilerOptions']['annotateForClosureCompiler'] = false;
+    // Note: It's important that the "expectedOut" is only modified in a way that still
+    // keeps posix normalized paths. Otherwise this could cause unexpected behavior because
+    // ngc-wrapped is expecting POSIX paths and the TypeScript Bazel rules by default only pass
+    // POSIX paths as well.
     data['angularCompilerOptions']['expectedOut'] =
         data['angularCompilerOptions']['expectedOut'].map(
-            f => f.replace(/\.closure\.js$/, '.js').replace(binDir, path.join(binDir, newRoot)));
+            f => f.replace(/\.closure\.js$/, '.js').replace(binDir, newOutputBase));
   }
   fs.writeFileSync(output, JSON.stringify(data));
 }