diff --git a/test/plugin.test.ts b/test/plugin.test.ts
index 693c594..f7e2e32 100644
--- a/test/plugin.test.ts
+++ b/test/plugin.test.ts
@@ -1203,13 +1203,13 @@ describe('Options', () => {
           writeToDisk: true,
         });
 
-        const spy = vi.spyOn(compiler.outputFileSystem, 'writeFile');
+        const spy = vi.spyOn(compiler.outputFileSystem!, 'writeFile');
 
         await run();
 
         expect(spy).toHaveBeenCalled();
 
-        const content = (await promisify(compiler.outputFileSystem.readFile)(manifest.getOutputPath()))?.toString();
+        const content = (await promisify(compiler.outputFileSystem!.readFile)(manifest.getOutputPath()))?.toString();
 
         expect(manifest.toString()).toEqual(content);
       });
diff --git a/test/utils.ts b/test/utils.ts
index f0ca295..4b66919 100644
--- a/test/utils.ts
+++ b/test/utils.ts
@@ -26,7 +26,8 @@ export function makeCompiler(configuration: Configuration): Compiler {
     ...configuration,
   });
 
-  compiler.outputFileSystem = createFsFromVolume(new Volume());
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  compiler.outputFileSystem = createFsFromVolume(new Volume()) as any;
 
   return compiler;
 }
@@ -47,7 +48,8 @@ export function makeMultiCompiler(configurations: Configuration[]): MultiCompile
     ),
   );
 
-  compiler.outputFileSystem = createFsFromVolume(new Volume());
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  compiler.outputFileSystem = createFsFromVolume(new Volume()) as any;
 
   return compiler;
 }