diff --git a/packages/ngtools/webpack/src/angular_compiler_plugin.ts b/packages/ngtools/webpack/src/angular_compiler_plugin.ts
index 34183aef51..663476531c 100644
--- a/packages/ngtools/webpack/src/angular_compiler_plugin.ts
+++ b/packages/ngtools/webpack/src/angular_compiler_plugin.ts
@@ -911,18 +911,18 @@ export class AngularCompilerPlugin {
         // When Ivy is enabled we need to add the fields added by NGCC
         // to take precedence over the provided mainFields.
         // NGCC adds fields in package.json suffixed with '_ivy_ngcc'
-        // Example: module -> module__ivy_ngcc
+        // Example: module -> module_ivy_ngcc
         // tslint:disable-next-line:no-any
         (compiler as any).resolverFactory.hooks.resolveOptions
           .for('normal')
           // tslint:disable-next-line:no-any
           .tap('WebpackOptionsApply', (resolveOptions: any) => {
-            const mainFields = (resolveOptions.mainFields as string[])
-              .map(f => [`${f}_ivy_ngcc`, f]);
+            const originalMainFields: string[] = resolveOptions.mainFields;
+            const ivyMainFields = originalMainFields.map(f => `${f}_ivy_ngcc`);
 
             return {
               ...resolveOptions,
-              mainFields: flattenArray(mainFields),
+              mainFields: [...ivyMainFields, ...originalMainFields],
             };
           });
       }